High bandwidth binary multi-leaf collimator design

ABSTRACT

Described herein are multi-leaf collimators that comprise leaf drive mechanisms. The leaf drive mechanisms can be used in binary multi-leaf collimators used in emission-guided radiation therapy. One variation of a multi-leaf collimator comprises a pneumatics-based leaf drive mechanism. Another variation of a multi-leaf collimator comprises a spring-based leaf drive mechanism having a spring resonator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/173,824, filed Jun. 10, 2015 and U.S. Provisional PatentApplication No. 62/335,571, filed May 12, 2016, the disclosures of whichare hereby incorporated by reference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made in part during work supported by grant number2R44CA153466-02A1 from the National Cancer Institute. The government mayhave certain rights in the invention.

BACKGROUND

Radiation therapy seeks to ablate tumor tissue using high-energyradiation such as X-rays. Radiation treatment plans are designed tobalance the need to apply a sufficient dose of radiation to the entiretumor tissue volume with the need to apply as little radiation aspossible so as not to damage healthy tissue surrounding the tumor.However, because treatment plans and the tumor images on which they arebased are devised far in advance of the treatment session, the treatmentplan may not account for changes in the tumor geometry and/or patientanatomy.

Furthermore, during a radiation therapy treatment session, minute tumorand/or patient movements may unintentionally expose non-tumorous tissueto radiation. Accordingly, radiation treatment systems that canprecisely irradiate tumor tissue based on real-time tumor and patientdata may be desirable.

BRIEF SUMMARY

Described herein are various mechanisms that may be suitable for use ina high-bandwidth multi-leaf collimator for an emission guided radiationtherapy system. Emission guided radiation therapy (EGRT) systems may beconfigured to direct radiation to a tumor volume based on real-timetumor data, such as the location data of gamma ray photon emissions froma radioactive tracer accumulated in a tumor. EGRT systems are configuredto apply a beam of radiation shortly after an emission is detected. Anyof the high-bandwidth multi-leaf collimators described herein may beused in an EGRT system to reduce the latency between emission detectionand radiation application. The mechanisms described below may facilitatethe rapid and reliable movement of collimator leaves such that thecollimator is capable of transitioning leaves between open and closedstates in about 10 ms or less, e.g., about 8 ms or less, about 7 ms orless, about 6 ms or less, about 4 ms or less. Some variations ofhigh-speed, high-bandwidth collimators may comprise one or morecam-based systems, spring systems, fluid-power (e.g., pneumatic)systems, slotted-link (e.g., scotch yoke) systems, and/orelectromagnetic systems. In addition to mechanisms that facilitate rapidleaf movement, some multi-leaf collimators may optionally comprisereduced-weight leaves where only the material in the radiation beam pathhave high-Z materials, and the peripheral support structure(s) of theleaves comprises lighter-weight materials. Also disclosed herein areleaf arrangements that may help reduce the friction between leaves, aswell as ways to package and arrange the various leaf drive mechanisms sothat the collimator is suitable for mounting on a rotatable gantry.

Also disclosed herein is a collimator that may comprise a leaf movablebetween a first location and a second location, a leaf shaft having aproximal portion and a distal portion that is attached to the leaf, aspring system coupled to the leaf shaft and configured to apply forcesalong a longitudinal axis of the leaf shaft, and an actuator systemcoupled to the leaf shaft. The forces applied by the spring system andthe actuator system on the leaf shaft may longitudinally translate theleaf shaft to move the leaf between the first and second locations, andthe actuator system may be configured to selectively retain the leaf atthe first location or the second location. The actuator system may beconfigured to supply a motive force sufficient to overcome losses in thespring system. The actuator system may comprise a first configurationwhere the leaf is retained in the first location and a secondconfiguration where the leaf is retained in the second location. Thespring system may comprise at least one coil spring or torsion barspring. When the actuator system is in the first configuration, the leafmay be in a closed configuration and when the actuator system is in thesecond configuration, the leaf may be in an open configuration, and thespring system and actuator system may be configured to transition theleaf between the closed configuration and open configuration in about 6ms or less.

In some variations, the actuator system may comprise a barrel comprisinga longitudinal lumen, a first side opening, and a second side opening,and a piston extends within the longitudinal lumen of the barrel. Thepiston may comprise the shaft and a piston seal coupled to the shaftwithin the barrel. Movement of the piston within the barrel maytranslate the leaf between the first location and the second location.The spring system may comprise a first spring disposed along a firstlength of the shaft on a first side of the piston seal, and a secondspring disposed along a second length of the shaft on a second side ofthe piston seal that is opposite the first side. The first and secondsprings may be configured such that the piston seal moves between thefirst opening and the second opening. In some variations, the firstspring and the second spring may be located within the barrel lumen andoptionally, the first spring may be in contact with the piston seal onthe first side and the second spring may be in contact with the pistonseal on the second side. In another variation, the first spring may belocated outside of the barrel lumen between a spring retainer and afirst end wall of the barrel and the second spring may be locatedoutside of the barrel lumen between a second end wall of the barrel andthe leaf. A collimator may also comprise a fluid source connected to thefirst opening and the second opening, where the movement of the pistonis controlled by fluid flow into and/or out of the first and secondopenings. For example, an actuator system may further comprise a firstvalve between the first opening and the fluid source and a second valvebetween the second opening and the fluid source, where the first andsecond valves selectively regulate fluid flow into and out of the barrellumen. The fluid source may be a pressurized air source. The actuatorsystem may be configured such that injecting fluid from the fluid sourceto the second opening and not the first opening causes the piston tomove the leaf to the second location. Sufficient amounts of fluidinjected into the second opening may create sufficient pressure to holdthe leaf in the second location. The piston seal may be configured tocontact the first spring and not the second spring when the leaf is inthe first location and to contact the second spring and not the firstspring when the leaf is in the second location. Some variations maycomprise a controller in communication with the fluid source, the firstvalve and the second valve. The controller may be configured to open andclose the first valve and the second valve to selectively regulate fluidflow into and out of the barrel lumen. The controller may be configuredto move the leaf to the first location by opening the first valve andclosing the second valve. Optionally, the controller may be configuredto open the second valve to vent the fluid (e.g., to atmosphericpressure) prior to opening the first valve and then closing the secondvalve after the leaf has been moved to the first location. Thecontroller may also be configured to move the leaf to the secondlocation by opening the second valve and closing the first valve. Insome variations, the controller may be configured to open the firstvalve to vent the fluid (e.g., to atmospheric pressure) prior to openingthe second valve and then closing the first valve after the leaf hasbeen moved to the second location.

In another variation of a collimator comprising a leaf, a leaf shaft, aspring system and an actuator system, the proximal portion of the leafshaft may comprise a slot and the actuator system may comprise a motor,a rod, a crank rotatably connected to the rod, and a roller connected tothe crank. The roller may rotatably translate within the slot, and therotation of the roller may be controlled at least in part by the motorvia the rod and crank and at least in part by spring forces applied bythe spring system on the leaf shaft. The crank may have a longitudinalaxis and the arm may have a longitudinal axis, and when the longitudinalaxis of the crank is aligned with the longitudinal axis of the leafshaft, the leaf may be retained at either the first location or thesecond location. The slot may have a vertical dimension and a horizontaldimension, where the vertical dimension may be greater than thehorizontal dimension. For example, the slot may be shaped as an oval orellipse, and/or may have two parallel vertical sides. The slot may havean oval-like shape that has a plurality of curves and/or lobes havingdifferent radii of curvature. In some variations, the slot may have afirst curved region, a second curved region and a third curved region.The first, second and third curved regions may be contiguous with eachother. When the roller is located in the first curved region, springforces from the spring system may cause the leaf to move between thefirst location and the second location. When the roller is located inthe second curved region, rotation of the roller within the slot may notcause translation of the leaf shaft and the leaf may be retained ineither the first location or the second location. When the roller islocated in the third curved region, rotation of the roller further intothe region may compress the spring at a nonlinear rate. In somevariations, the slot may be bilaterally symmetric about a vertical axissuch that there is a first side and a second side symmetric to the firstside, and the first, second and third curved regions may be located onthe first side and fourth, fifth, and sixth curved regions thatcorrespond to the first, second and third curved regions may be locatedon the second side. When the roller is located in the second or thirdcurved regions of the first side of the slot, the leaf may be retainedin an open position and when the roller is located in the fifth or sixthregions of the second side of the slot, the leaf may be retained in aclosed position. The spring system may comprise a torsion bar spring,and the torsion bar spring may optionally be connected to the leaf shaftby a pivotable coupling arm such that rotational torsion of the barspring causes the leaf shaft to translate longitudinally. A first end ofthe pivotable coupling arm may be connected to the torsion bar springvia a pin and a second end of the pivotable coupling arm may beconnected to the arm via a second ball bearing. Alternatively, thespring system may comprise one or more coil springs. For example, thespring mechanism may comprise a first coil spring and a second coilspring, where the first coil spring is biased such that it applies aforce to the leaf shaft such that the leaf moves toward the firstlocation and the second coil spring is biased such that it applies aforces to the leaf shaft such that the leaf moves toward the secondlocation. The actuator system may be located at a central portion of theleaf shaft, and the first coil spring may be wrapped around a firstlength of the leaf shaft proximal to the actuator system and the secondcoil spring may be wrapped round a second length of the arm distal tothe actuator mechanism.

Some variations of an actuator system that may be used in a collimatormay comprise a first electromagnet and a second electromagnet separatedby a space from the first electromagnet, and a ferromagnetic membermovable across the space between the first and second electromagnets.The leaf shaft may be connected to the movable member, and the actuatorsystem may further comprise a first configuration where either the firstor second electromagnet is activated such that the movable member issecured at the location of either the first or second electromagnet, anda second configuration where the first and second electromagnets arealternately activated such that the movable member is movable within thespace. Each of the first and second electromagnets may comprise a pairof adjacent coil windings and a U-shaped core extending through thelumens of both of the coil windings. In some variations, the movablemember may comprise a permanent magnet. Alternatively or additionally,the actuator system may comprise a linear actuator, such as a voicecoil.

One variation of a multi-leaf collimator may comprise a leaftranslatable between an open position and a closed position, a camassembly, and a latch that selectively engages the cam assembly with theleaf. The latch may have a locked configuration where the cam assemblyis engaged with the leaf such that movement of the cam assembly causesmovement of the leaf, and an unlocked configuration where the camassembly is disengaged from the leaf such that movement of the camassembly does not cause movement of the leaf. In the closed position,the leaf may be located in a radiation path of a radiation source, andin the open position, the leaf may not be in the radiation path of theradiation source. The cam assembly may comprise a cam and a follower,and when in the locked configuration, rotating the cam may transitionthe leaf between the closed position and the open position. In somevariations, a shaft may be attached to the leaf, and the latch mayselectively engage the follower with the shaft such that in the lockedconfiguration, the follower and the shaft are mechanically engaged, andin the unlocked configuration, the follower and the shaft aremechanically disengaged. The latch may be coaxial with the shaft. Insome variations, the latch may comprise an outer housing attached to thefollower and an inner cylindrical member rotatably mounted within theouter housing, and the inner member may be rotatably engaged with theshaft. The outer surface of the inner member may comprise a first set ofsplines and the inner surface of the outer housing may comprise a secondset of splines that may be aligned with the first set of splines whenthe latch is in the locked configuration. The first set of splines andthe second set of splines may be radially arranged.

Some variations of a multi-leaf collimator may also comprise a rotaryactuator configured to transition the latch between the unlockedconfiguration and the locked configuration. The rotary actuator maycomprise an actuator shaft that may be coaxial with the latch andcoupled to the latch via a connector, and rotation of the actuator shaftmay transition the latch between the locked configuration and theunlocked configuration. The connector may be attached to the innercylindrical member and the outer surface of the connector may comprise athird set of splines, and the inner surface of the outer housing maycomprise a fourth set of splines configured to interlock with the thirdset of splines to select a relative rotational position of the connectorwith respect to the latch. In some variations, the third set of splinesand the fourth set of splines may be radially arranged such that theyare radially interlocked. Optionally, a spring assembly may be coupledto the actuator shaft, where the spring assembly may be configured totransition the latch between the locked and unlocked configurationsfaster than the rotational speed of the rotary actuator. The springassembly may comprise one or more torsion springs. In some variations, alinear actuator may be included and configured to transition the latchbetween the unlocked configuration and the locked configuration. Somevariations may also comprise a spring configured to bias the leaf to theclosed configuration. The cam may have two or three lobes, as may bedesirable. Optionally, a multi-leaf collimator may comprise a secondlatch mechanism configured such that the leaf is in the openconfiguration independent of the cam position.

Another variation of a system for selectively moving a leaf between afirst position and a second position may comprise an arm carrying theleaf, a rotating cam, a cam follower engaged with the cam, and a latchfor selectively coupling the motion of the cam follower to the arm, suchthat when the latch is locked, the cam follower causes the arm to movethe leaf from the first position to the second position. The system mayfurther include a spring arranged to move the leaf from the secondposition back to the first position. In some variations, the latch mayinclude a cylindrical outer member having a set of radially disposed,internally projecting splines and a cylindrical inner member having aset of radially disposed, externally projecting second splines. When thelatch is in an unlocked position the first and second splines may beradially offset allowing the first splines to slidably telescope withrespect to the second splines and when the latch is in a lockedposition, the end faces of the first splines may abut the end faces ofthe second splines causing the arm to move the leaf from the firstposition to the second position.

Another variation of a system for selectively moving a leaf between afirst and a second position may comprise a spring system for supplyingthe force to move the leaf between a first and a second position, and anactuator system for latching or holding the leaf in a selected positionand for supplying a motive force sufficient to overcome losses in thespring system. The spring system may include one or more springs wherethe zero-force position of the one or more springs corresponds to alocation when the leaf is between the first and second positions. Thespring system and actuator system may be arranged to reciprocate theleaf between the first and second positions and the actuator system maybe employed to prevent the leaf from moving from the first to the secondposition or from the second position to the first position. In somevariations, the actuator system may not be used to hold the leaf when itreaches one position when it is desired to immediately thereafter movethe leaf to the other position. The spring system may be designed tomove the leaf beyond the first and second positions so that that theleaf will be located in the open and closed positions for apredetermined dwell time.

Another variation of a system for selectively moving a leaf between anopen and a closed position may comprise a spring system forreciprocating the leaf between a first and second positions, an actuatorsystem comprising a secondary drive mechanism coupled to the leaf tosupply motive force sufficient to overcome losses in the spring system,and a phase shifting mechanism for adjusting the movement of the leaf tochange the timing of the arrival of the leaf to the first and secondpositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic depiction of one variation of an emission guidedradiation therapy system.

FIG. 2 is a schematic depiction of one variation of a cam-based leafdrive mechanism that may be used in a collimator.

FIG. 3A is a perspective view of one variation of a cam-based leaf drivemechanism that may be used in a collimator. FIG. 3B is a perspective andpartial cutaway view of a latch mechanism of the cam-based leaf drivemechanism of FIG. 3A. FIGS. 3C and 3D are perspective exploded componentviews of the latch mechanism of FIG. 3B. FIG. 3E is a perspectivecross-sectional view of the latch mechanism of FIG. 3B. FIG. 3F is aperspective cross-sectional view of a component of the latch mechanismof FIG. 3B. FIG. 3G is an end view of a component of the latch mechanismof FIG. 3B. FIGS. 3H and 3I are perspective partial cutaway views of thelatch mechanism of FIG. 3B in the locked (FIG. 3H) and unlocked (FIG.3I) configurations. FIGS. 3J and 3K are views of another variation of alatch mechanism. FIG. 3L is a perspective exploded component view of atorsion spring assembly of a cam-based leaf drive mechanism. FIG. 3M isa timing diagram that outlines the sequence of events before, during andafter a latch transition.

FIG. 4 is a perspective view of another variation of a cam-based leafdrive mechanism.

FIG. 5 is a perspective view of one variation of a package of cam-basedleaf drive mechanisms.

FIGS. 6A and 6B are side views of some variations of collimator leaves.FIGS. 6C and 6D are side views of some variations of collimator leaveswith weights to adjust the location of the center of mass.

FIGS. 7A and 7B are schematic depictions of one variations of aspring-based leaf drive mechanism, where the top depiction is a view ofthe drive mechanism from a beam's eye view and the bottom depiction is aside view (i.e. view axis is perpendicular to the beam's eye view). FIG.7C is a schematic depiction of another variation of a spring-based leafdrive mechanism. FIG. 7D is an alternate view of the spring-based leafdrive mechanism of FIG. 7C.

FIGS. 8A-8C schematically depict one variation of a latch that may beused with a spring-based leaf drive mechanism.

FIGS. 9A-9D depict timing diagrams of one variation of a phase-shiftedspring-based leaf drive mechanism. FIGS. 9E and 9F schematically depictone variation of a phase-shifted spring-based leaf drive mechanism. FIG.9G depicts a timing diagram of another variation of a spring-based leafdrive mechanism.

FIG. 10A depicts one variation of a pneumatic leaf drive mechanism.FIGS. 10B-10F depict different states of one variation of a pneumaticleaf drive mechanism. FIG. 10G depicts a timing diagram of the pneumaticleaf drive mechanism of FIGS. 10B-10F. FIGS. 10H and 10I are schematicend views of one variation of a piston of a pneumatic leaf drivemechanism.

FIGS. 11A-11F depict one variation of a leaf actuation system comprisinga slotted-link or scotch yoke mechanism. FIGS. 11B, 11D, 11F areclose-up depictions of the different configurations of the scotch yokemechanism as the leaf moves between a closed and an open configuration.

FIG. 12A is a perspective component view of the coupling between theroller, the crank, and the distal-most end of the motor shaft. FIG. 12Bis a partial exploded view of the assembly in FIG. 12A. FIG. 12C is across-sectional view of the assembly of FIG. 12A.

FIGS. 13A-13B depict one variation of a slot of a scotch yoke mechanism.

FIG. 14A depicts a variation of a slot of a scotch yoke mechanism. FIG.14B another variation of a slot of a scotch yoke mechanism.

FIG. 15A is a perspective component view of one variation of acollimator leaf drive mechanism comprising a spring system and anactuator system including a scotch yoke or slotted link mechanism. FIG.15B is an alternate perspective component view of the leaf drivemechanism of FIG. 15A. FIG. 15C is a top perspective view of a pluralityof collimator leaf drive mechanisms assembled/packaged together. FIG.15D depicts a side perspective view of the plurality of collimator leafdrive mechanisms of FIG. 15C. FIGS. 15E-15G depict a flowchartrepresentation of a method for assembling a plurality of leaf drivemechanisms that comprise a spring system and an actuator systemincluding a scotch yoke, FIG. 15H depicts an elevated perspective viewof the plurality of leaf drive mechanisms of FIG. 15C.

FIG. 16A is a perspective view of a collimator leaf drive mechanismcomprising a pneumatic actuator system. FIG. 16B depicts across-sectional view of the pneumatic actuator system of FIG. 16A. FIGS.16C-16E depicts the pneumatic actuator system of FIG. 16A as the leafmoves between the closed configuration and the open configuration. FIG.16F depicts a variation of a pneumatic system where the spring system islocated outside of the barrel. FIG. 16G depicts a plurality of pneumaticactuator systems assembled/packaged together. FIG. 16H depicts onevariation of a pneumatic actuator system comprising one or more bumpersor dampers.

FIG. 17A is a perspective view of a collimator leaf drive mechanismcomprising an electromagnetic actuator system. FIG. 17B is a side viewof the electromagnetic actuator system of FIG. 17A. FIG. 17C is across-sectional view of the electromagnetic actuator system of FIG. 17Ctaken along line A-A in FIG. 17D. FIG. 17D is an alternate side view ofthe electromagnetic actuator system of FIG. 17A. FIG. 17E is aperspective view of one variation of a collimator leaf drive mechanismcomprising an electromagnetic actuator system similar to that of FIG.17A.

FIG. 18A is a perspective view of another variation of a collimator leafdrive mechanism comprising an electromagnetic actuator system. FIG. 18Bis a side view of the electromagnetic actuator system of FIG. 18A.

FIGS. 19A-19C depict variations of electromagnetic actuator systems.

FIG. 20A is a schematic representation of collimator leaves at variouspositions and FIG. 20B depicts a timing diagram used by a leafcontroller to attain the leaf positions depicted in FIG. 20A.

DETAILED DESCRIPTION

Disclosed herein are various drive mechanisms that may be suitable foruse in a multi-leaf collimator. Such leaf drive mechanisms mayfacilitate the rapid and reliable movement of collimator leaves suchthat the collimator is capable of transitioning leaves between open andclosed positions in about 10 ms or less, e.g., about 4 ms or less.Various leaf drive mechanisms are described below, including cam-baseddrive mechanisms, spring-based drive mechanisms, fluid-power drivemechanisms, and/or electromagnetic drive mechanisms. In addition toincreasing the speed of leaf movement by increasing the speed of theleaf drive mechanisms, some multi-leaf collimators may optionallycomprise reduced-weight leaves where only the material in the radiationbeam path have high-Z materials (e.g., tungsten), and the peripheralsupport structure(s) of the leaves comprises lighter-weight materials.Also disclosed herein are leaf arrangements that may help reduce thefriction between leaves, as well as ways to package and arrange thevarious leaf drive mechanisms so that the collimator is suitable formounting on a rotatable gantry.

While the leaf drive mechanisms disclosed herein are described in thecontext of a binary multi-leaf collimator for collimating a radiationbeam, it should be understood that these drive mechanisms may be used inother types of collimators and furthermore, are not limited tocollimator technology. Any of the leaf drive mechanisms described hereinmay be used in collimators for conformal radiation therapy, emissionguided radiation therapy (EGRT), and intensity modulated radiationtherapy (IMRT). Certain of these leaf drive mechanisms may be suitablefor use in other mechanical systems. The speeds and rates of operationof any of the drive mechanisms described herein may also vary from thespeeds and rates described in the examples. For example, while the leafdrive mechanisms are described as being capable of transitioning leaves(for example, leaves having a radiation-attenuating portion have alength of about 10 cm, width of about 1 cm, and a thickness of about 3mm thick) between open and closed states in about 10 milliseconds orless, the leaf transition time may be from about 2 milliseconds to about10 seconds.

One variation of a system that may comprise any of the multi-leafcollimators as described herein is depicted in FIG. 1. The radiationtherapy system may comprise a plurality of gamma ray photon emissiondetectors (e.g., positron emission detectors) located on a first gantry.The gantry may be stationary or may be rotatable. The radiation therapysystem may also comprise a rotatable radiation source (e.g., a linearaccelerator or linac). The rotatable radiation source may be located onthe same gantry as the gamma ray photon emission detectors, or may belocated on a different gantry (i.e., a second gantry) that may berotated independently from the first gantry. There may also be an X-raydetector located on the second gantry across from the radiation source.Before a treatment session, a patient may be injected with a radioactivetracer. In some variations, the tracer may be a PET tracer such asfluorodeoxyglucose (FDG) that accumulates at a tumor site. Gamma rayphotons (e.g., a pair of photons emitted from a positron annihilationevent) may be emitted from the tumor site and detected by the gamma rayphoton detectors. When the photons are detected, the radiation sourcemay be rotated and positioned such that a radiation beam may be directedtoward the tumor site with respect to the gamma ray photon emissionpath. A multi-leaf collimator, such as any of the collimators describedherein, may be disposed in the beam path and used to further shape thebeam and/or select the beamlet. In some variations, by positioning theradiation source and opening and closing selected leaves of thecollimator, the radiation beam may be directed approximately along thedetected photon emission path. The radiation beam may be applied withina short period of time after the gamma ray photons are detected, forexample, within 0.25 seconds of detecting the photons. This may help tocompensate for motion artifacts that may arise from breathing and/orinadvertent patient movement. In some variations, the radiation beam maybe applied before the tumor moves substantially, and/or before an imagebased on the gamma ray photon emission path is formed. Directing aradiation beam with respect to a detected gamma ray photon emission pathwithout generating an image based on that detected photon may help toincrease the likelihood that radiation is applied to the tumor sitebefore it moves substantially. This in turn may help to reduce theradiation exposure of peripheral healthy tissue (e.g., tissue close tothe tumor boundary), as well as to reduce the length of the treatmentsession. Additional description of a radiation therapy system isprovided in U.S. Pat. No. 8,017,915, filed Feb. 9, 2009, which is herebyincorporated by reference in its entirety. Any of the collimatorsdescribed herein may be included in a radiation therapy system (e.g., anemission guided radiation therapy system) to facilitate dynamic,real-time selection of radiation beamlets and/or direction of radiationto a tumor site. For example, the positions of the collimator leaves maybe adjusted while the radiation source and collimator are rotating. Thecollimator may be disposed in the beam path or fan beam of the radiationsource and may, in some variations, be located within the same housingor module as the radiation source. Alternatively, a collimator may bedisposed external to the radiation source housing or module.

One way to direct radiation to a tumor site before it moves, and/or toapply radiation to a tumor site within a short period of time (e.g.,less than about 2 seconds, about 1 second, about 0.5 second, or about0.25 second) after detecting the photon emissions may comprise rotatingthe radiation source at speeds greater than current radiation therapygantries. For example, current gantries rotate at about 1 rpm, while anEGRT gantry on which the radiation source is mounted may rotate betweenabout 10 rpm to about 70 rpm (e.g., about 30 rpm, about 60 rpm), and insome variations, faster than 70 rpm. In addition to increasing therotation speed of the gantry, the associated collimator mounted on thegantry may also operate at a higher frequency than current collimators.For example, the collimator may operate at a speed such that thecollimator leaves may transition from an open position (i.e., permittingthe passage of a radiation beamlet) to a closed configuration (i.e.,blocking the passage of a radiation beamlet) in about 10 ms or less(e.g., about 4 ms or less). As an illustration, a radiation therapysystem having 100 locations around the gantry from which the radiationsource may fire a beam (i.e., 100 firing locations) may have a radiationsource gantry that is configured to rotate at a speed of 60 rpm. In thisvariation, the collimator leaves of the radiation source may beconfigured to open or close in about 10 ms or less. In a system withmore firing locations, for example 250 firing locations where the gantryrotates at 60 rpm, the collimator leaves of the radiation source may beconfigured to open or close within about 4 ms or less. If the rotationsource gantry (note that there may be any number of radiation firingpositions around the radiation source gantry, for example, about 60firing positions, 120 firing positions, 250 firing positions, etc.) wereto rotate faster than 60 rpm, e.g., 70 rpm or 75 rpm, the collimatorleaves may be configured to open or close in even shorter periods oftime, e.g., less than 4 ms, about 3 ms, about 2 ms, about 1 ms or less.In some variations, the bandwidth or the maximum frequency of operationof a collimator may be about 50 Hz, or even greater than about 50 Hz.That is, the inverse of the shortest time period it takes for a leaf totransition from a closed position to the open position and then back tothe closed position, or from an open position to the closed position andthen back to the open position may be about 50 Hz or more. For example,for a radiation source gantry that rotates at 75 rpm, a collimator leafmay be configured to transition between open and closed positions withinabout 8 ms (about 62.5 Hz) for 100 firing locations and within about 3.2ms (about 156.25 Hz) for 250 firing locations. In some variations, aleaf may be moved at a speed from about 50 cm/s to about 400 cm/s. Thecollimator leaf drive mechanisms described herein may be suitable foroperating at such high speeds and frequencies for real-time irradiationof a tumor, and may, for example, be compactly packaged for mounting ona rotating gantry.

Optionally, the collimator leaves described herein may comprise aradiation-attenuation structure and optionally a support structureattached to the radiation-attenuation structure. When the leaf is in theclosed position, the radiation-attenuation structure is located in theradiation beam path. The radiation-attenuation portion may be made of ahigh-Z material (e.g., a high atomic numbered material). Optionally, acollimator leaf may additionally comprise a support structure thatcouples the radiation-attenuation structure with a leaf drive mechanismand/or other components in the collimator. The support structure maycomprise a frame of beams, bars, rods, and/or brackets that may help tovertically stabilize the leaf as it moves in a horizontal direction intoand out of the beam path, and may optionally contain leaf guides and/orpush rods. In some variations, the support structure may comprise atruss framework. The support structure may optionally include openings,hooks, notches, protrusions, grooves, and the like so that a leaf drivemechanism may be attached to the collimator leaf. A support structuremay also comprise notches, protrusions, grooves, ridges, etc. thatcorrespond with similar structures in a leaf guide, which may help theleaf move along a path. The size and shape of the leaves of a multi-leafcollimator for radiation therapy may be at least partially determined bythe geometry of the gantry and/or the width of the radiation beam and/orthe desired “resolution” at which radiation is to be applied (e.g.,slice width, number of slices). The depth of the leaves may besufficiently thick to impede the transmission of radiation when theleaves are in the closed position. For example, a leaf made of a high-Zmaterial such as tungsten may be about 10 cm deep or more. Thecollimators described herein may have 64 leaves, but it should beunderstood that the number of leaves may be varied, e.g., 12, 15, 16,24, 25, 31, 32, 36, 48, 50, 64, 72, 75, 100, 101, 128, 135, etc. Thewidth of the individual leaves of a 64-leaf collimator may be from about1 mm to about 10 mm, e.g., about 2 mm. The length of leaf travel (e.g.,the slice size) may be from about 0.25 cm to about 3 cm, e.g., about 1cm. The smaller the travel range, the more precisely the radiation maybe delivered. Reducing leaf travel length or width may prolong patienttreatment time. The mass of the radiation-attenuation portion of a leafmay be from about 2.5 grams to about 100 grams, e.g., about 30 grams.The support structure of a leaf may have a mass from about 10 grams toabout 100 grams, e.g., about 20 grams. As such, the total mass of acollimator leaf may be from about 13 grams to about 200 grams, e.g.,about 50 grams. Moving leaves of this mass at the bandwidths describedabove may be challenging for current collimators, but may be attained bythe high-bandwidth collimators described herein.

Disclosed herein are various leaf drive mechanisms that may be used in ahigh-bandwidth collimator. The described leaf drive mechanisms may becapable of moving individual collimator leaves at a speed from about 50cm/s to about 400 cm/s. In a binary multi-leaf collimator, these drivemechanisms may translate the leaf between a closed position, where theleaf is located in the path of a radiation beam, and an open position,where the leaf is not located in the path of the radiation beam. In somevariations, a collimator may comprise a leaf drive mechanism thatcomprises a cam and follower to translate the leaf between an openposition and a closed position. Another variation of a leaf drivemechanism may comprise one or more springs that apply force(s) on theleaf to transition between an open position and a closed position. Forexample, a leaf may be coupled to a spring resonator that translates theleaf between an open position and a closed position. In anothervariation, a leaf drive mechanism may comprise fluid-power components,for example, a hydraulic or pneumatic driven piston in a cylinder. Thepiston and cylinder may have corresponding non-circular cross-sections.The cylinder may have one or more valves that may be independentlycontrolled to regulate the flow and/or pressure of fluid therein.Alternatively or additionally, any of the collimator leaf drivemechanisms described herein may comprise one or more springs to move theleaf to a closed position or open position. These drive mechanisms maybe configured to move each leaf of a multi-collimator individuallyand/or independently, or may be configured to move two or more leavestogether.

Optionally, the leaves and their corresponding drive mechanisms may bearranged such that two leaves may be adjacent to each other, but offsetin the vertical direction (e.g., in the direction of the radiationbeam). This allows the width of the actuators driving the leaves to bewider than the leaves, while still allowing the actuators to drive theleaves along their center of mass. A multi-leaf collimator may alsocomprise a plurality of leaf guides that correspond with each of theleaves to limit the movement of the leaves along a linear path thatcrosses (e.g., is transverse to) the beam path.

In addition or alternatively to increasing the speed of the leaftransitions by using faster drive mechanisms, some variations ofmulti-leaf collimators may comprise leaves where only the portion of theleaf that is in the radiation path when the leaf is in the closedposition is made of a radiation-impermeable material, while theremaining portion of the leaf may be made of other materials, e.g.,materials that are less dense and/or lighter than theradiation-impermeable materials. For example, the portion of the leafthat is in the radiation path when the leaf is in the closed positionmay be made of tungsten, while the remainder of the leaf, including thesupport/frame to which the leaf is attached is made of much lightermaterials, such as stainless steel or titanium. In some variations,removing or hollowing out regions of the radiation-impermeable materialmay help to reduce the weight of the radiation-impermeable portion withlittle or no impact to the ability of the leaf to impede radiationtransmission. For example, the portion of the radiation-impermeableportion of the leaf that is in the radiation path may be substantiallysolid, while the portion of the radiation-impermeable portion of theleaf that is not in the radiation path may have one or more hollowregions.

Optionally, a multi-leaf collimator may comprise one or more position,velocity, acceleration or force sensors configured to detect theposition, velocity, acceleration or force of each of the leaves, and toprovide such data to a controller. It may be useful to select a sensorthat is capable of providing precise data in high-radiationenvironments, such as a capacitance-based position sensor. Otherexamples of sensors that may be used in any of the multi-leafcollimators and/or drive mechanisms described herein may include anopto-electronic interrupter. The data from the one or more sensors maybe included in a feedback control algorithm stored and executed in thecontroller to monitor and/or regulate the precision and speed of theleaf movement. The feedback control algorithm may also factor in therotation of the gantry and the radial location of the radiation sourceand collimator when providing the commands to the leaf actuators.

FIG. 2 is a schematic depiction of a cam-based leaf drive mechanism 200that may be included in a collimator disposed in the beam path of aradiation source (e.g., for a radiation therapy system). The cam-basedleaf drive mechanism 200 may comprise a cam 202, a follower 204, apushrod or shaft 210 attached to a side of a leaf 206, a clutch 208 thatselectively engages or disengages the follower and the shaft, and aspring 212 attached to the opposite side of the leaf 206. The cam 202may be a constant rotation cam (e.g., the cam is continuously rotated)that drives a follower. The follower 204 may be coupled to the leaf 206,where the clutch or latch 208 determines whether the leaf 206 moves inconcert with the follower 204. As depicted in FIG. 2, the follower maybe coupled to the leaf 206 via a shaft or pushrod 210. The shaft orpushrod 210 may be made of a low-Z material that does not interfere withthe radiation beam from the radiation source. An actuator (e.g. a piezoactuator; not shown) may be coupled to the clutch 208 and used tocontrol whether the clutch is 208 engaged or disengaged. When the clutch208 is disengaged, the position of the leaf is controlled by the spring212, which pushes on the leaf in the direction of arrow 213 and biasesthe leaf to a closed position 214. The leaf can be held in the closedposition 214 because the cam follower 204 slides inside the shaft 210,and does not apply a force on the leaf (e.g., not moving the leaf). Whenthe clutch 208 is engaged, the cam follower 204 becomes rigidly attachedto the shaft 210 and rotation of the cam 202 moves the leaf against theforce of the spring 212 in the direction of arrow 211, therebycompressing the spring 212 and moving the leaf to an open position 216.Due to the constantly rotating cam 202, however, the leaf cannot remainin an open position 216 when the clutch 208 is engaged, since rotatingthe cam 202 will cause the leaf to open, then close and then open againas the cam 202 rotates. The duration of time that the leaf spends in theopen position 216 may be adjusted, for example, by adjusting the arc ofthe cam lobe to adjust the dwell time (e.g., increasing the arc of thelobe may increase the dwell time).

One variation of a cam-based leaf drive mechanism for a multi-leafcollimator that may be included in a radiation therapy system isdepicted in FIGS. 3A-3K. FIG. 3A depicts a cam-based drive mechanism 300comprising a leaf 302, a shaft 308 connected to the leaf, a cam 304, afollower 306 that is in contact with the cam and selectively engaged tothe shaft 308, a latch 310 configured to selectively engage the followerand the shaft, and a solenoid or rotary actuator 312 coupled to thelatch 310 and configured to control whether the latch engages thefollower with the shaft or disengages the shaft from the follower. Insome variations, the cam-based drive mechanism may also comprise atorsion spring assembly 307 that may be arranged to couple the rotaryactuator 312 to an actuator shaft 309 to facilitate and/or expeditetransitioning the latch 310 between a first locked configuration (wherethe leaf shaft 308 and the follower 306 are engaged and locked togethersuch that movement of the follower causes a corresponding movement inthe shaft) and a second unlocked configuration (where the leaf shaft 308and the follower 306 are disengaged and unlocked from each other suchthat movement of the follower does not cause a corresponding movement inthe shaft). Optionally, the cam-based leaf drive mechanism 300 maycomprise a shaft guide 314 disposed over the shaft 308 and configured tostabilize the leaf shaft 308 such that the shaft is translated in alinear path. The leaf drive mechanism 300 may optionally comprisedistal-most springs 316 that may apply a spring force on the leaf 302 inthe direction of arrow 317. Moving the leaf 302 in the direction ofarrow 317 moves the leaf into the closed position (i.e., into theradiation beam path). When the cam cycles to a lift event (i.e., where alobe of the cam contacts the follower) and the follower is engaged withthe leaf shaft 308, the leaf 302 may be moved to an open position (i.e.,away from, and/or out of, the radiation beam path), which is in thedirection denoted by arrow 319. The cam may have one, two, three or morelobes, as may be desirable. The cam may be configured to be continuouslyrotated, for example, by a rotary actuator (not shown). By constantlyrotating the cam and only switching the latch to selectively engage theleaf when the follower is in the base-circle region of the cam, the highbandwidth element (the latch) and the high force element (the cam) areactuated separately. This separation means the high bandwidth elementcan operate on a smaller mass and smaller distance instead of having toact very quickly on a larger mass. In some variations, a cam may havethree lobes and may rotate at 2000 rpm such that there are 100 liftevents per second (i.e., 100 Hz). The latch may be capable oftransitioning between the engaged and disengaged states in about 1 ms orless. In other variations, the cam may rotate at less than 2000 rpm, andmay rotate at 1000 rpm, 100 rpm or 10 rpm. One or more lubricants may beprovided between the moving parts of this (and other) leaf drivemechanisms to facilitate the movement of the different components and toreduce the effects of frictional forces. In some variations, thelubricant may be resistant to depletion by radiation (e.g., aradiation-hard lubricant). Optionally, the leaf drive mechanisms may beenclosed in a sealed housing so that the lubricant within the box doesnot leak out.

The location of the leaf 302 may be determined by the sum of thepush-pull forces exerted upon the leaf 302 and/or the leaf shaft 308 bythe distal-most springs 316 and the cam 304. The distal-most springs 316may apply a pushing force on the leaf (i.e., in a direction indicated byarrow 317 in FIG. 3A), which may bias the leaf into the closedconfiguration. The cam 304 and follower 306 may apply a pulling force onthe leaf (i.e., in a direction indicated by arrow 319) when the latch310 engages or locks the follower 306 with the leaf shaft 308 and a lobeof the cam is in contact with the follower (i.e., a lift event). Thepulling force in the direction of arrow 319 may be greater than the pushforce of the distal-most springs in the direction of arrow 317,resulting in a net pulling force that translates the leaf into the openposition (i.e., net movement in the direction of arrow 319). As the camrotates and the follower is no longer riding on a lobe of the cam, thepulling force is reduced and the pushing force of the distal-mostsprings dominates, thereby translating the leaf to the closed position(i.e., net movement in the direction of arrow 317). When the latch 310is switched such that the follower 306 is disengaged or unlocked fromthe leaf shaft 308, the movement and position of the leaf is notcontrolled by the cam 304, but is instead biased by the distal-mostsprings 316 into the closed position. Continued rotation of the cam maycontinue to drive the follower 316, the motion of which applies a forceagainst the proximal springs 318 (a.k.a. lost-motion springs). However,once the latch 310 is switched such that the follower 306 is engaged orlocked with the leaf shaft 308, the leaf 302 may be translated betweenthe open and closed positions in accordance with the rotation of the camand movement of the follower.

Different types of latches may be used to selectively engage thefollower with the shaft. One variation of a latch mechanism is depictedin FIGS. 3B-3I. As depicted in FIGS. 3B-3F, the latch mechanism 310 maycomprise an elongate tube 330 having a lumen 332 therethrough and one ormore protrusions or splines 334 along the interior wall of the lumen, aninner ring 336 with one or more protrusions or splines 338 on its outersurface that correspond to the protrusions 334 of the tube lumen 332,where the inner ring 336 is rotatable with respect to the elongate tube330, an actuator shaft 309 connected to the inner ring 336, and a rotarymotor 312 that is arranged to rotate the actuator shaft 309 such thatthe inner ring 336 rotates within the elongate tube. A partial cutawayview of the elongate tube 330 and an end view of the elongate tube aredepicted in FIGS. 3F-3G, and a perspective view of the inner ring 336 isdepicted in FIG. 3D. As depicted in FIG. 3G, the protrusions 334 alongthe inner surface of the elongate tube lumen 332 may be radiallyarranged and the protrusions 338 of the inner ring 336 may be radiallyarranged in corresponding fashion. The edges of the protrusions may becurved or rounded, which may help to ease the stresses on theprotrusions as the inner ring rotates with respect to the elongate tube.Optionally, a lubricant may be provided between the components of thelatch, such as between the protrusions of the inner ring and theelongate tube. There may be any number of protrusions 334 on the innersurface of the elongate tube lumen 332 and the outer surface of theinner ring 336, for example, 2, 3, 4, 5, 6, 8, 10, 12, 14, 20, etc. Thevariations depicted in FIGS. 3D and 3F have 12 protrusions. The innerring 336 may be rotatably connected to the leaf shaft 308 which drivesthe leaf 302 between the open and closed positions. One example of theconnectivity between the inner ring 336, leaf shaft 308, and latchmechanism 310 is depicted in FIGS. 3C, 3D, and 3I. The elongate tube 330may be connected to a portion of the follower 306 by contacting thedistal surface of the tube 331 to a surface 333 of the follower that islocated along the linear path along with the leaf shaft 308 translates,as depicted in FIG. 3B. Rotation of the actuator shaft 309 by therotator motor 312 transitions the latch 310 between a first lockedconfiguration where the end faces of the protrusions 338 of the innerring are aligned with the end faces of protrusions 334 of the tube lumen332 (depicted in FIG. 3H) and a second unlocked configuration where theend faces of protrusions 338 of the inner ring are not aligned with theend faces of protrusions 334 of the tube lumen (depicted in FIG. 3I). Inthe second configuration, the protrusions 338 of the inner ring 336 maybe located in the spaces between the protrusions 334 of the tube. In thefirst configuration, as depicted in FIG. 3H, the opposing contactbetween the end faces of the protrusions of the inner ring and theelongate tube transfers the force and movement of the follower to theleaf shaft, such that the shaft is linearly translated as the cam drivesthe follower. The follower may pivot during the lift events, thepivoting of which translates to a linear motion of the leaf shaft. Inthe second configuration, as depicted in FIG. 3I, the end faces of theprotrusions of the inner ring and the elongate tube are no longer inface to face opposing contact, and the protrusions 334 of the elongatetube are slidably received in the space between the protrusions 338 ofthe inner ring. Accordingly, the force and movement of the follower 306is not transferred to the leaf shaft 308, and the elongate tube slipswith respect to the inner ring as the cam drives the follower.

One variation of how the inner ring of a latch mechanism may berotatably coupled to the leaf shaft is depicted in FIGS. 3C-3E. As shownin FIG. 3D, a plug 340 may be inserted through the opening 337 of theinner ring 336 and inserted into a lumen 339 of the leaf shaft 308. Theplug 340 may be fixably attached to the leaf shaft 308, for example, byfriction welding, or laser welding, such that the inner ring 336 iscaptured between the proximal end 343 of the plug 340 and the proximalend of the leaf shaft. The diameter of the body 341 of the plug may beless than the diameter of the ring opening 337, which may allow theinner ring to rotate with respect to the plug 340 and the leaf shaft308, but the widened proximal end 343 of the plug captures the innerring 336 against the leaf shaft 308. The inner ring may be rotatablycoupled to the leaf shaft in other ways, for example, as depicted inFIGS. 3J-K and described in more detail below.

Rotation of the inner ring 336 may be driven by the rotary motor via theactuator shaft. One variation of how the actuator shaft 309 may becoupled to the inner ring is depicted in FIG. 3E. As shown there, theactuator shaft may be attached to the inner ring 336 using a tubularconnector 342, where one end of the tubular connector (e.g., the distalend 344) is attached to the inner ring 336 and the other end of thetubular connector (e.g., the proximal end 346) is attached to theactuator shaft 309. For example, a lumen 348 of the tubular connectormay be sized and shaped at the distal end 344 to accommodate a proximalcollar of the inner ring 336 and/or the plug 340 such that the tubularconnector 342 may be friction fit with the collar of the inner ring. Thelumen 348 of the tubular connector may be sized and shaped at theproximal end to accommodate the distal end of the actuator shaft suchthat the tubular connector 342 may be a sliding fit with the actuatorshaft such that rotating the actuator shaft rotates the tubularconnector and the actuator shaft can slide axially inside the tubularconnector. The tubular connector and the inner ring may be coupled suchthat rotation of the tubular connector by the actuator shaft causes acorresponding rotation of the inner ring. In some variations, thetubular connector and the inner ring are rotatable with respect to theleaf shaft and the plug.

The tubular connector 342 may attach the actuator shaft 309 to the innerring 336 inside the lumen 332 of the elongate tube 330. Some variationsof a tubular connector 342 may comprise features that may help to retainits rotational orientation with respect to the elongate tube 330. Forexample, as depicted in FIG. 3F, the inner surface of the elongate tube330 may comprise a second set of protrusions or splines 350 proximal tothe first set of protrusions 334 (i.e., the protrusions 334 thatcorrespond with the protrusions of the inner ring 336), and the outersurface of the tubular connector 342 may comprise one or moreprotrusions 352 that correspond to the second set of protrusions 350.There may be any number of protrusions on the inner surface of theelongate tube lumen and on the outer surface of the tubular connector,for example, 2, 3, 4, 5, 6, 8, 10, 12, 14, 20, etc. The variationsdepicted in FIGS. 3D and 3F have 6 protrusions. These protrusions orsplines may act as rotary stops as the actuator shaft 309 rotates theinner ring 336 to transition the latch mechanism between the firstconfiguration (i.e., where the motion of the leaf shaft is locked to themotion of the follower) and the second configuration (i.e., where themotion of the leaf shaft is not locked to the motion of the follower).The protrusions 352 on the outer surface of the tubular connector 342may be angularly offset from the protrusions 338 on the outer surface ofthe inner ring 336, as depicted in FIGS. 3E, 3H, 3I, such that when theprotrusions 352 of the tubular connector are at a first rotary positionwith respect to the protrusions 350 of the elongate tube 330, the latchis in the first locked configuration and when the protrusions 352 are ata second rotary position with respect to the protrusions 350, the latchis in the second unlocked configuration. A rotary position is one inwhich the protrusions 352 are located in the spaces between protrusions350 and vice versa. That is, in the first rotary position, the end facesof protrusions 338 of the inner ring are aligned with the end faces ofthe protrusions 334 of the tube lumen 332 (e.g., the protrusions 338abut the protrusions 334, as depicted in FIG. 3H). In the second rotaryposition, the end faces of protrusions 338 of the inner ring are notaligned with the end faces of the protrusions 334 of the tube lumen 332(e.g., the protrusions 338 are instead located in the spaces between theprotrusions 334, as depicted in FIG. 3I). In use, the tubular connector342 may be rotated in a first direction (e.g., clockwise) to transitionthe latch from the first locked configuration to the second unlockedconfiguration and rotated in a second direction opposite the firstdirection (e.g., counterclockwise) to transition the latch from thesecond unlocked configuration to the first locked configuration.Alternatively in some variations, the tubular connector 342 may berotated in a single direction to transition the latch between the firstlocked configuration and the second unlocked configuration, where eachrotary stop transitions the latch (i.e., every other rotary stopcorresponds to the first locked configuration and the remaining otherrotary stops correspond to the second unlocked configuration).

The travel angle (i.e., the rotation angle needed to move from thelocked configuration to the unlocked configuration) may depend at leastin part on the number and size of the first set of protrusions. Forexample, the first set of protrusions 334 of the elongate tube 330 maycomprise 12 protrusions, where each protrusion occupies an angular sweepof about 15 degrees, and the space between protrusions occupies anangular sweep of about 15 degrees. This spacing of protrusions would bethe same for the protrusions 338 of the inner ring 336, and the travelangle would be 15 degrees, as this is the angle required to move theprotrusions 338 from alignment with protrusions 334 (corresponding tothe first locked state), to mesh with protrusions 334 so that theprotrusions 338 align with spaces between the protrusions 334 and thusslide axially (corresponding to the second unlocked state). The secondset of protrusions 352 of the elongate tube 330 which correspond withprotrusions 352 of the tubular connector 342 may have an angular sweepthat is different from the angular sweep of the first set of protrusions334, so that the tubular connector 342 can be rotated with respect tothe elongate tube 330 through the travel angle. For example, the secondset of protrusions may have six protrusions 350 having an angular sweepof 15 degrees with a space between protrusions of 45 degrees, but theprotrusions 352 on the tubular connector 342 may have an angular sweepof 30 degrees with a space between the protrusions of 30 degrees. Theprotrusions 352 on the tubular connector 342 would be axially alignedwith, and have the same angular sweep as the protrusions 350 on theelongate tube 330. The protrusions 352 on tubular connector 342 areoffset (center to center) by 22.5 degrees from the protrusions 338 ofthe inner ring 336. The protrusions 352 fit in the space betweenprotrusions 350, and are thus able to rotate through the 45−30=15degrees of the travel angle. This rotation, in which a protrusion 352moves from contact with one protrusion 350 to contact with theneighboring/adjacent protrusion 350, causes alignment or meshing ofprotrusions 338 and protrusions 334, and thus transition between thelocked and unlocked configurations. The rotation that gives rise tothese transitions may occur during the base-circle portion of the camrotation, because only then are the protrusions 334 and protrusions 338axially displaced from each other.

Another variation of the coupling between the actuator shaft, latch, andleaf shaft is depicted in FIGS. 3J-3K. As depicted there, there may be asingle tubular connector 370 with a central lumen 373, where the distalend of the lumen is configured to couple with the leaf shaft 376 and theproximal end of the lumen is configured to couple with the actuatorshaft 378. The tubular connector 370 may be located within the lumen ofan elongate tube 371, which may be similar to the elongate tube 330 aspreviously described. The tubular connector 370 may comprise a first setof protrusions 372 that are distal to a second set of protrusions 374,where the first set of protrusions 372 may be similar to the protrusions338 of the inner ring and the second set of protrusions 374 may besimilar to the protrusions 352 of the tubular connector. The elongatetube 370, like the elongate tube 330 of the previous variation, may alsocomprise a first set of protrusions that correspond with (e.g.,complementary to) the first set of protrusions 372 of the tubularconnector and a second set of protrusions that correspond with (e.g.,complementary to) the second set of protrusions 374. The tubularconnector 370 may comprise a recess or grooved region 380 at a proximalportion of the lumen 373, which recess is configured with a stop toaxially retain the leaf shaft 376 such that the tubular connector isrotatable with respect to the leaf shaft, but does not move axially(e.g., laterally) with respect to the leaf shaft. For example, thetubular connector 370 and the leaf shaft 376 may be coupled using athreaded interface. A threaded interface may permit some small axialtranslation of the tubular connector 370 with respect to the leaf shaft376 during rotation of the tubular connector. This small translation canbe allowed for by properly sizing the axial gap in the elongate tube 370so as to ensure that the translation does not itself engage or disengagethe distal protrusions 372 and their complementary protrusions on theelongate tube. Unlike the previous variation depicted in FIGS. 3B-I,this variation has fewer separate parts and avoids the need to weld orotherwise rigidly join parts, which may help to simplify themanufacturing and assembly process.

In some variations, it may be desirable to reduce the time it takes thelatch mechanism to transition between the first locked configuration andthe second locked configuration. For example, it may be desirable forthe latch to switch from the first configuration to the secondconfiguration in the base circle duration, and/or be able to switch inless than about 10 ms, e.g., less than about 1 ms. In some variations, ahigh-speed selectively-switchable latch mechanism for a cam and followerleaf drive mechanism may have a torsion spring assembly that may beconfigured to allow a solenoid to move during the lift event tocharge-up a helical torsion spring, and then during the base circleduration (the non-motion period of the cam and follower cycle) thetorsion spring may cause rotary motion of the tubular connector. Due tothe small rotational inertia of the rotary latch, a helical torsionspring may cause latch or un-latch motion in less than 1 ms whereas thefastest electro-mechanical devices cannot perform the same rotary motionwith the same rotational inertia in less than 1 ms. Reducing theduration time to engage or disengage the latch increases the durationtime for the motion of the shaft. In some variations, a torsion springassembly may switch the latch in less than 10 ms, which may allow thelatch to operate at frequencies greater than 50 Hz. One variation of atorsion spring assembly that may help to increase the switch speed ofthe latch is depicted in FIG. 3L. As shown there, a torsion springassembly 400 may comprise a proximal stop piece 402, a middle stop piece404, a distal stop piece 406, a first torsion spring 408 located betweenthe proximal stop piece 402 and the middle stop piece 404 and a secondtorsion spring 410 located between the distal stop piece 406 and themiddle stop piece 404. The proximal, middle and distal stop pieces mayeach comprise an opening (403 a,b,c) and are arranged such that theopenings of all of the stop pieces and the openings (405 a,b) of thefirst and second torsion springs 408, 410 may be aligned and coaxialwith an actuator shaft 413 (which may be similarly arranged to theactuator shaft 309 depicted in FIGS. 3A-B). The middle stop piece 404may have a first lip or collar 414 a on a proximal side configured tofit with the opening 403 a of the proximal stop piece 402 and a secondlip or collar 414 b on a distal side configured to fit with the opening403 c of the distal stop piece 406. The opening 403 a of the proximalstop piece 402 may be sized and shaped to fit with a solenoid shaft 416of the solenoid or rotary actuator 412 such that the solenoid shaft 416is coupled to the proximal stop piece 402. The proximal stop piece 402may have one or more protrusions or rotary stop features that correspondwith one or more protrusions or rotary stop features on a proximalsurface of the middle stop piece 404. The opening 403 c of the distalstop piece may be sized and shaped to fit with the actuator shaft 413such that the actuator shaft is coupled to the distal stop piece 406.The distal stop piece 406 may have one or more protrusions or rotarystop features that correspond with one or more protrusions or rotarystop features on the distal surface of the middle stop piece 404. Theactuator shaft 413 may extend through and may be coupled to the distalstop piece 406, and the opening 403 b in the middle stop piece 404 maybe sized and shaped to fit with the actuator shaft 413 so that themiddle stop piece 404 can rotate freely on the actuator shaft 413. Theactuator shaft 413 may extend through the middle stop piece 404, and theopening 403 a on the proximal stop piece 402 may be sized and shaped tofit the actuator shaft 413 so that the proximal stop piece 402 that iscoupled to the solenoid shaft 416 may rotate freely on the actuatorshaft. Rotation of the solenoid shaft 416 by the rotary actuator 412during a cam lift event may charge up the first torsion spring 408, andcause it to propel the switching of the inner ring from the firstconfiguration to the second configuration during the cam base cycleduration by causing a rotation of the middle stop piece 404 such thatthe rotary stop features of the middle stop piece 404 engage the rotarystop features of the distal stop piece 408 and cause it and the actuatorshaft 413 to rotate. Rotation of the solenoid shaft 416 by the rotaryactuator 412 in the opposite direction during a cam lift event may causethe rotary stop features of the proximal stop piece 402 and the middlestop piece 404 to engage, rotating the middle stop piece 404 and causingit to charge of the second torsion spring 410. This may cause the secondtorsion spring 410 to propel the switching of the inner ring from thesecond configuration to the first configuration by rotating the distalstop piece 406 and the coupled actuator shaft. The motion of the rotaryactuator/motor 412 that occurs during a cam lift event may cause atleast one of the torsion springs to “charge up” (i.e., retain potentialenergy). The retained potential energy is then released in order toquickly switch the latch from one configuration to the other. As can beappreciated, during a cam lift event, the end faces of splines 338 and334 on the inner ring 336 and the elongate tube 330 respectively willeither be (a) lined up and pushing on one another to move the leaf inthe direction of arrow 319 (open) or (b) they will be “meshed” orinterleaved and telescopingly sliding past each other to take up all thecam motion, with the spring 316 returning the leaf to the closedposition. The torsional springs of the torsional spring assembly mayallow the rotary actuator 312/412 to start moving ahead while the cam isstill in the lift event to prepare for the next state transition duringthe next base circle event. These torsional springs “load up” during thelift event, building up a torque on the latch. The torque cannot movethe latch during the lift event, because either (a) there may be toomuch friction on the splines to allow rotation or (b) the mesh of thesplines may prevent rotation. But as soon as the latch becomes unloadedand the splines separate axially, the springs can snap the latch to thenew configuration. So the torsional spring assembly may help to lengthenthe time for the rotary actuator to add energy into the system toexecute the latch transition in the very short time allowed by the basecircle duration of the cam. The torsional springs may also allow for avery short base circle, and therefore more cam angle devoted to the liftevent, which may result in smoother lift event accelerations.

The operation of this variation of the cam-based leaf drive mechanismcan be further explained by reference to FIG. 3M, which is one variationof a timing diagram showing the interaction between the cam, rotaryactuator, rotational position of the inner ring member, and the springsof the torsion spring assembly. In this variation, the leaf transitiontime (e.g., the time it takes for a leaf to transition from the firstlocked configuration to second unlocked configuration, or vice versa)may be about 8 ms, and the time in which the leaf may remain in the openposition may be about 2 ms (e.g., this may correspond to the dwell timeof the cam). The timing diagram of FIG. 3M illustrates the sequence ofevents that leads to the transition of the latch from an unlockedconfiguration to a locked configuration and back to the unlockedconfiguration within a 10 ms period (e.g., where the latch is locked forjust one lift event), so that the leaf is in the open position by timepoint t₁, which occurs during lift event L2. The first row representsthe cyclical rotation of the continuously rotating cam, where a liftevent occurs as the cam rotates, causing the follower to translate from0 mm to 9 mm at it moves from the base circle of the cam up the camlobe. The base circle duration is the time in which the follower isriding along the base circle radius, and is the time in which the latchcan most readily transition between the locked and unlockedconfigurations. In this example, the base circle duration is about 1.5ms. During the lift event L1 prior to the target lift event L2, therotary actuator or solenoid may begin to rotate the solenoid shaft 15degrees or more in a first direction, as depicted in the second row ofthe timing diagram. As the solenoid shaft rotates in the firstdirection, torsion spring A (e.g., the proximal torsion spring 408) maybe “charged” such that potential energy is stored in the spring. Thetorsion spring A may be prevented from releasing the stored potentialenergy due to the frictional forces between the splines of the innerring and the elongate tube or the interleaving of the splines. Once thecam rotates through the lift event L1 and begins the base cycle durationat time point t₂, splines of the inner ring and the elongate tube are nolonger in contact (e.g., friction between them is zero or no longermeshed or interleaved), and the stored potential energy in torsionspring A may be released, thereby rotating the actuator shaft andtransitioning the latch from the unlocked configuration (at 0 degrees)to the locked configuration (at 15 degrees), as depicted in the thirdrow of the timing diagram. This transition may occur within 1.5 ms, forexample, in about 0.5 ms to about 0.8 ms. Once the latch is in thelocked configuration, the leaf shaft moves in concert with the cam andfollower, so that during lift event L2, by time point t₁, the leaf maybe in the open position. To transition the latch back to the unlockedconfiguration by lift event L3, the solenoid may begin to rotate in asecond direction opposite to the first direction during lift event L2,depicted as the negative slope in the second row of the timing diagram.This rotation may charge torsion spring B (e.g., the distal spring 410)such that potential energy is stored in the spring. Once the cam rotatesthrough the lift event L2 and begins the base cycle duration at timepoint t₃, the stored potential energy in torsion spring B may bereleased, thereby rotating the actuator shaft and transitioning thelatch from the locked configuration (at 15 degrees) to the unlockedconfiguration (at 0 degrees), depicted as the negative slope in thethird row of the timing diagram. This transition may occur within 1.5ms, for example, in about 0.5 ms to about 0.8 ms.

One variation of a cam-based actuator that may be used to retain theleaf in the open configuration may comprise two cams having lobes thatare offset such that the movement of the followers that they each driveare out-of-phase with each other. That is, when a first follower isriding on a lobe of the first cam, a second follower is not riding onthe lobe of the second cam and vice versa. For example, a cam-baseddrive mechanism used to transition a leaf between an open position and aclosed position may comprise a first cam having two lobes and acorresponding first follower, a second cam having two lobes and acorresponding second follower, wherein the lobes of the second cam are90 degrees offset from the lobes of the first cam, and a plurality oflatch mechanisms that selectively connects either the first follower orthe second follower to the leaf shaft. Each cam supports opening a leafat every other firing position, so to transition a leaf from closed toopen at a given firing position for the gantry, one of the two cams willbe utilized to provide the motive force for the leaf, and to transitionfrom closed to open at the neighboring firing position, the other camwould be utilized. To retain the leaf in the open position, a top latchis engaged to hold the shaft to which the leaf is connected, and bothcam latches are dis-engaged. To move a leaf, the leaf may be alternatelyconnected to the first cam and follower and the second cam and followerduring the dwell time of each of the cams (i.e., the duration of timewhen a lobe of the cam is contacting the follower), such that as thedwell time for one cam ends, the leaf shaft is disengaged from thatfollower and engaged to other follower as the dwell time for the othercam begins. One example of such a cam-based drive mechanism is depictedin FIG. 4. This variation of a cam-based drive mechanism 450 comprises afirst cam 452 having two lobes, a first follower 454 in contact with thefirst cam 452, a second cam 456 having two lobes positioned such thatthe two lobes are 90 degrees offset with respect to the lobes of thefirst cam 452, a second follower 458 in contact with the second cam 456,a first latch 460 that selectively engages the first follower 454 withthe leaf shaft 451, a second latch 462 that selectively engages thesecond follower 458 to the leaf shaft 451. Optionally, the cam-basedleaf drive mechanism 450 may comprise a first shaft guide 453 locatedadjacent to the first latch 460 and a second shaft guide 455 locatedadjacent to the second latch 462. The cam-based drive mechanism may alsocomprise a first rotary actuator 470 and a second rotary actuator 472that are each configured to transition the first latch and the secondlatch respectively between a first configuration where the follower isengaged with the leaf shaft and a second configuration where thefollower is disengaged from the leaf shaft. The structures of the cams,followers, latches, torsion spring assembly, and rotary actuators may besimilar to the corresponding components described above. The first andsecond rotary actuators may be controlled (e.g., using controllersoftware) such that either the first latch is in the first configurationor the second latch is in the first configuration, but not both.Optionally, in some variations, a third latch 474 and third rotaryactuator 476 may help to ensure that only one cam/follower pair drivesthe leaf shaft at a time.

The cam-based leaf drive mechanism (and any of the leaf drive mechanismsdescribed herein) may be wider than the leaf itself. For example, acam-based leaf drive mechanism may have a width from about 4 mm to about6 mm, while the width of a leaf may be about 1 mm to about 2 mm. Assuch, it may be difficult to arrange the leaves to be adjacent to eachother, with little or no space between leaves, since in doing so, therewould not be enough space to accommodate the drive mechanisms that drivethe leaves. Some variations of a multi-leaf collimator may be configuredto actuate the leaves from both sides of the multi-leaf collimator andstaggering the drive mechanisms vertically, so that the actuation isapplied at different points for neighboring leaves (i.e., not along thecenter of mass of the leaf). However, at the high speeds of the leafmotion described herein, it may be helpful or desirable to actuate eachleaf at or near (e.g., exactly along) the center of mass of the leaf, soas to not induce unwanted moments on the leaf. Such moments can causeoscillatory modes or vibrations, or cause binding in the leaf guides.FIG. 5 depicts one variation in which 64 leaves may be packaged suchthat the collimator leaves may be adjacent to each other and canaccommodate each of the leaf actuators while providing for actuationthrough each leaf's center of mass. Collimator assembly 500 may comprisea first leaf 502, a second leaf 504 that is adjacent to the first leaf,and a third leaf 506 that is adjacent to the second leaf. The movementof the first leaf 502 may be driven by a first actuator 503 and themovement of the second leaf 504 may be driven be a second actuator 505.The first actuator 503 may be on one side (e.g., the left side) whilethe second actuator 505 may be on the opposite side (e.g., on the rightside). Both the first and second actuators and first and second leavesmay be at the same vertical height or location (i.e., the tops of thefirst and second leaves may be aligned). The third leaf 506 may be at adifferent vertical height or location from the first and second leaves,and may be driven by a third actuator 507. The third actuator 507 may beon the same side as the first actuator 503 (e.g., on the left side), butat a different vertical height or location (e.g., lower than the firstactuator 503, as depicted in FIG. 5). A fourth leaf (not depicted) maybe at the same vertical height as the third leaf 506 and driven by afourth actuator located on the opposite side (e.g., right side) as thethird actuator 507. As depicted in FIG. 5, in addition to staggering oroffsetting the drive mechanisms in the vertical direction (i.e., alongor parallel to the radiation beam path), the leaves themselves may alsobe staggered or offset in the vertical direction. That is, cumulativelyover the 64 leaves, the leaves may be offset such that the first andsecond leaves may be at a first vertical location, third and fourthleaves at a second vertical location lower than the first verticallocation, the fifth and sixth leaves at the first vertical location, theseventh and eighth leaves at the second vertical location, and so on(e.g., vertical height of the leaves would be staggered such that thefirst eight leaves would be high, high, low, low, high, high, low, low,and so on). There may be any number of vertical positions across whichthe leaves may be staggered. Every other leaf coming from the same sideof the collimator may be in a higher vertical position and every otherleaf coming from the same side of the collimator may be in a lowervertical position, which may similarly shift the center of mass of theleaves in the vertical direction. In order to drive the leaves througheach leaf's center of mass, the drive mechanisms may be similarlyvertically shifted. Such vertical shifts to the leaves and the leafdrive mechanisms may provide enough horizontal space to accommodate thewidth of the drive mechanism. Although FIG. 5 depicts a collimatorcomprising a cam-based drive mechanism, it should be understood thatthis arrangement may be used with any of the leaf drive mechanismsdisclosed herein.

The collimator leaves in FIG. 5 and depicted herein in other drawingsare depicted as being identical to each other and linearly arranged suchthat the top edge of each of the leaves is generally orthogonal to aradiation beam path from a radiation source. In such arrangement, theleaves may not be equidistant from the radiation source. Since theradiation typically emanates from a point or spot source (the linearaccelerator target), the depth of each of the leaves (i.e., thedimension that is generally aligned with the direction of the radiationbeam) and the width of each of the leaves (i.e., the dimension that isgenerally orthogonal to the direction of the radiation beam) may varyacross the collimator, depending on the location of the leaf withrespect to the radiation source. For example, the collimator leaves mayhave an asymmetric shape (when viewed from the side), where the parallelsides are the top and bottom sides of the leaf. The total length of thetop edges of the leaves may be smaller than the total length of thebottom edge of the leaves, such as is depicted in FIG. 6A. The width ofeach of the leaves may be thicker or thinner at the left and right sidesof the collimator than in the center of the collimator, to allow formore coarse or more precise delivery of radiation in different regionsof the gantry bore.

In other variations, collimator leaves may be arranged such that eachleaf is equidistant from the radiation source. For example, thecollimator leaves may form an arc or curve with respect to the beampath, as depicted in FIG. 6B. Each of the leaves may be a substantiallysymmetric trapezoid (e.g. isosceles trapezoid) and may have varyingdepths and widths.

With the varying geometry of the leaves (e.g., asymmetric or symmetrictrapezoidal leaves), it may be difficult to effectively verticallystagger the position of the leaves in the manner described above to beable to fit the leaf drive mechanisms together while also keeping theleaves in apposition with each other and having the drive mechanismdrive the leaf at its center of mass. One variation of an arrangement ofleaves and leaf drive mechanisms that may address these issues isschematically depicted in FIG. 6C, which depicts a side schematic viewof a trapezoidal leaf assembly 602 comprising a leaf 601 (e.g., theportion of the leaf assembly made of a radiation impermeable materialand/or enters the radiation beam path) where the bottom base portion 604is wider (i.e., more massive) than the top base portion 606. Althoughtrapezoidal-shaped leaves are described here, it should be understoodthat the leaves may have any desirable geometry, some of which may ormay not have their center of mass located at a geometric center or axisof symmetry of the leaf. As shown FIG. 6C, a leaf drive mechanism 600(e.g., any of the mechanisms described herein) may linearly translate aleaf along its center of mass via a leaf shaft 608. The center of massof a leaf may vary depending on the shape of a leaf and in some cases,may not be at the geometric center of the leaf. For example, thetrapezoidal leaf 602 may have a center of mass that is lower (e.g.,closer to the bottom edge) than a rectangular leaf. A weight 610 havinga particular mass may be placed at various locations on the leaf and/orthe frame or support structure attached to the leaf to adjust thelocation of the center of mass. For example, the weight 610 may beplaced higher up on a trapezoidal leaf 602 in order to raise thelocation of the center of mass so that it is closer to the geometriccenter 612 or to the top base portion of the leaf. The location wherethe shaft connects to the leaf, and therefore the location where theleaf drive mechanism drives the leaf may vary according to the locationof the center of mass, which may be adjusted by the addition of one ormore weights 610. While the weight 610 may be located on aradiation-permeable region of the leaf, the weight 610 may also belocated on the radiation-impermeable region of the leaf, as shown inFIG. 6D. FIG. 6D depicts a trapezoidal leaf 622 connected by a shaft 628to a leaf actuator 620 that may be any of the leaf drive mechanismsdescribed herein. A weight 610 may be included on theradiation-impermeable portion of the leaf that may help to adjust thecenter of mass towards the top of the leaf 622. Alternatively oradditionally, portions of the leaf and/or leaf assembly may be cut orhollowed out to adjust the location of the center of mass. The locationsof the center of mass for differently shaped leaves of a multi-leafcollimator may vary, and the locations of the actuators may also varysuch that they are vertically staggered. Vertically staggering theactuators may provide more space in the horizontal direction tosufficiently accommodate the array of actuators that drive the array ofleaves.

Some variations of a leaf drive mechanism of a collimator included in aradiation therapy system (e.g., the emission guided radiation therapysystem of FIG. 1) may comprise a spring system comprising one or moresprings to transition the leaf between the open position and the closedposition. Optionally, a leaf drive mechanism may further comprise anactuator system, which may include a latching mechanism. In somevariations, spring-based leaf drive mechanisms may comprise a springsystem comprising one or more springs connected to the leaf and a latchto retain the leaf in the closed position or the open configuration. Theone or more springs may be coupled to both a stationary frame and amovable mass, coupled to only one of the stationary frame and movablemass, or simply be positioned between a stationary frame and a movablemass. Some spring systems may comprise a spring resonator. Differenttypes of springs may be used, as desired, for example, coil springs,torsion springs, torsion bars, leaf springs, flexure elements, and thelike. Springs with non-linear or step-wise linear spring constants mayalso be utilized to implement motion profiles other than pure sinusoids.Multiple springs may be used in parallel to generate sufficient force tomove the leaf. Spring-based leaf actuation systems may comprise a brakeor latch in order to capture and retain the leaf at a desired position(e.g., at the open position, closed position, the position where theleaf velocity is zero, the position where the maximum amount ofpotential energy is stored in the spring, etc.). Alternatively oradditionally, a drive mechanism may comprise an actuator system that iscoupled to the one or more springs (e.g., coupled to a moving massdisposed between two opposing springs and/or coupled to the spring nearwhere the spring attaches to a stationary support), to add a “booster”force while the springs are in motion, which may augment the primarymotive force provided by the spring system. An actuator system maycomprise any of the actuators described herein, including, but notlimited to, a pneumatic actuator, an electric motor (with or without aslotted-link mechanism), an electromagnetic voice-coil, a planaractuator, etc. Examples of suitable actuators may include linear orrotary actuators, and may be coupled to a transmission mechanism, e.g.rotary actuators coupled to a rack-and-pinion, etc. An actuator systemmay comprise an actuator and a brake/latch, which may optionally becombined into one unit or structure. In addition to restoring energylost due to friction, the actuator system could also be used to startthe system up from a de-energized state (when the leaf stationary at thecenter of travel) by exciting the spring resonator at the resonantfrequency until the desired motion amplitude is achieved. The actuatormay be coupled to the mount point of the spring, and may be configuredto add energy by compressing or extending the spring. Alternatively oradditionally, the actuator and/or latch may be coupled to the leaf.

In one variation, a spring-based leaf drive mechanism of a collimatorfor use in a radiation therapy system may comprise a support, one ormore springs attached between the leaf and the support such that thesprings apply forces to the leaf to translate the leaf between the openand closed positions, and a latch configured to capture the leaf at adesired position. One variation of a leaf-based leaf drive mechanism isdepicted in FIGS. 7A-7B. The leaf 700 is attached to a spring-baseddrive mechanism comprising one or more springs 702 where one end of thesprings is attached to a stationary support 704 and the other end of thesprings is attached to the leaf 700. The spring-based drive mechanismmay also comprise a latch or friction brake 706. In the variationdepicted in FIGS. 7A and 7B, the one or more springs 702 may apply aforce such that the leaf 700 is moved to the open position (FIG. 7A) orthe closed position (FIG. 7B). The latch 706 may be configured tocapture the leaf 700 to retain it at the open or the closed position,thereby retaining potential energy in the one or more springs 702. Whilethe one or more springs 702 are shown as comprising four springs, witheach spring used in both compression and extension, are depicted, such aspring mechanism may have any number of springs, for example, 1, 2, 3,4, 5, 6, 7, 8, 10, 12, etc. springs. The springs may all have the samespring constant, or may each have different spring constants. Thesprings may be used in any combination of compression and extension. Forexample, the one or more springs 702 may apply forces to the leaf 700 inboth compression and extension. The one or more springs 702 may beconfigured such that when the spring is compressed past a certainthreshold, potential energy is stored in the spring such that releasingthe spring from compression causes the spring to extend, and when thespring is extended or stretched past the threshold, potential energy isstored in the spring such that releasing the spring from extensioncauses the spring to compress. By operating the spring(s) 702 aroundthis threshold point, sufficient spring force (absent friction) isapplied to transition the leaf 700 between the open and closedpositions. In order to compensate for the loss of energy due tofriction, the spring-based leaf drive mechanism may comprise an actuatoror motor that is configured to add energy to the spring system. Forexample, an actuator may be coupled to the spring such that it appliesadditional compression or extension force to the spring to initiatespring movement from a stationary state and/or replenish energy lost inthe spring system due to friction or other energy loss mechanisms. Insome variations, the latch 706 may be configured to retain the leaf 700at a position where the potential energy stored in the spring(s) is at amaximum and/or when the potential energy stored in the spring(s) is at aminimum (i.e., zero), and/or at any point therebetween (i.e., where partof the energy in the spring(s) is stored in the spring as potentialenergy and part of the energy is released as kinetic energy that movesthe spring(s) at a non-zero velocity). For example, the latch may beconfigured to capture and retain the leaf when the leaf is at anextremum where the spring velocity is zero, and/or may be configured tocapture and retain the leaf when the leaf is not at an extremum, wherespring velocity is not zero.

Some spring systems of a leaf drive mechanism may comprise two sets ofopposing springs, where the opposing springs are attached to oppositesides of a movable mass, and the resonant motion of the mass between thesprings may drive the leaf between the open position and closedposition. In some variations, the spring system may comprise a firstspring (or set of springs) that may apply a force on the mass that movesthe leaf in a first direction towards the open position and a secondspring (or set of springs) that may apply a force on the mass that movesthe leaf in a second direction opposite to the first direction, wherethe second direction is towards the closed position. One or more latchesmay be located such that the leaf (and/or an additional mass, and/or asupport frame to which the leaf is attached) is captured and retained inthe open position and/or the closed position. For example, a first latchmay be located such that it is capable of capturing and retaining themovable mass such that the leaf is at the open position and a secondlatch may be located such that it is capable of capturing and retainingthe movable mass such that the leaf is at the closed position. In somevariations, the latch may be configured to retain the movable mass at aposition where the potential energy stored in the spring(s) is at amaximum and/or when the potential energy stored in the spring(s) is at aminimum (i.e., zero), and/or at any point therebetween. For example, thelatch may be configured to capture and retain the movable mass when theleaf is at an extremum where velocity is zero, and/or may be configuredto capture and retain the leaf when the leaf is not at an extremum,where velocity is not zero.

Alternatively or additionally, some spring-based leaf drive mechanismsof a collimator may comprise an actuator that is coupled to at least oneof the springs and/or the movable mass, where the actuator is configuredto compress and/or expand at least one spring to replace the energy lostin the system due to friction and/or latching at a non-zero velocity.For example, an actuator may act to compress a first spring when theleaf is in the closed position, so as to ensure the first spring hassufficient stored energy to fully transition the leaf to the openposition. In some variations, an actuator may be configured to addenergy to the spring mechanism by applying a force directly to themovable mass as it is moving. In some variations, the actuator may beconfigured to apply force to the spring at the resonant frequency of thespring system and/or in phase with the oscillation of the spring to addenergy to the spring system. For example, the actuator may be configuredto apply force to the spring when the sum of the potential and kineticenergy is below a usable limit (e.g. zero), as would be required to addenergy into the system to prepare it for use from an initial startupstate or to recover from an error. Alternately, the actuator may beconfigured to apply force to the spring at the moment when all of thespring energy has been converted to kinetic energy and/or duringcompression of the spring in order to store more potential energy in thespring. Alternatively or additionally, an actuator may be configured toadd energy to the spring mechanism when the mechanism is in the latchedstate, as depicted in FIGS. 7C and 7D and described below. In somevariations, the actuator may act directly on the spring, and not on themovable mass.

One variation of a spring-based leaf drive mechanism comprising a springsystem comprising a pair of springs is depicted in FIGS. 7C and 7D. Thespring-based leaf drive mechanism 720 may comprise a stationary support724, a movable support 725 of a selected mass to which the leaf 730 maybe attached, a first spring 722 attached between the stationary supportand the movable support, a second spring 726 attached between thestationary support and the movable support, a latch 728 configured tocapture and retain the leaf and/or movable support, and one or moreactuators 732 (e.g. piezo actuators) coupled between the springs and thestationary support. In some variations, the one or more actuators may becoupled to one or both of the springs. The latch 728 may be located suchthat it is capable of capturing the leaf 730 and/or movable support 725to retain the leaf in the open position. The actuator 732 may be a piezopusher which may further compress the second spring 726 to restore anyenergy lost due to friction and/or latching.

Different types of actuators may be used in a spring-based leaf drivemechanism to add energy back into the spring system. Some actuators mayact by directly applying force onto a spring, while some actuators mayact by directly applying force onto the movable mass, while still someother actuators may act by directly applying force to a leaf and/or leafsupport structure. Some actuators may be configured to fully compressand/or expand a spring (e.g. to initiate motion of non-moving leaf, suchas when the collimator first starts up or powers on, or when thecontroller has detected an error in the motion of the spring system andresets the springs to an initial, non-moving state), while otheractuators may be configured to apply a small amount of energy toinitiate spring motion and may apply a force at the resonant frequencyand in-phase with the oscillation of the spring system until the motionamplitude of the movable mass is at a desired amplitude, i.e.,sufficient to move the leaf to either the open position or the closedposition. Multiple actuators with different force capacities andfrequencies may be used with any of the spring-based drive mechanismsdescribed herein. Examples of actuator systems that may be used with aspring-based leaf drive mechanism may comprise electromagneticactuators, voice coil actuators, solenoid actuators, rotary actuators,linear actuators, pneumatic actuators, hydraulic actuators, ultrasonicactuators, combustive actuators, piezo actuators, electrostaticactuators and the like. In some variations, an actuator system maycomprise a latch or brake system. For example, an electromagnet (and/orin conjunction with a permanent magnet) may be configured to bothattract and repel the moving mass, to both capture and retain the leafand/or moving mass at a particular location and also to apply energyback into the system as needed. Similarly a pneumatic piston may beconfigured to push or pull the moving mass to retain the leaf at aparticular location and also to apply energy back into the system asneeded. Alternatively or additionally, a slotted link mechanism (e.g., ascotch yoke) may be used in conjunction with an electric motor or arotary solenoid actuator to capture and retain the leaf and/or movingmass at a particular location and also apply energy back into the systemas may be desired.

Various latches for capturing and retaining a movable mass and/or leafare described below. In some variations, a latch may capture and retaina movable mass and/or leaf by applying a force that opposes thedirection of movement of a leaf. For example, a latch may apply africtional force to the leaf, and/or apply a torque force that opposesthe direction of leaf movement. Examples of such latches may include anotch and following wheel, a releasable, overrunning clutch, and/or acapstan clutch (e.g., a torsion spring wrapped around axle). Forexample, a latch may comprise a releasable roller or “sprag” clutch tocapture the leaf upon motion reversal. A clutch may be designed toutilize capstan friction, in which a wire or thread is wrapped around acapstan that is coupled to the moving mass so that the capstan rotatesduring motion (e.g. with a rack and pinion assembly). Tensioning thewire or thread may exponentially increase the rotational friction on thecapstan, halting its motion. In some variations, a latch may have aretention feature and the moving mass and/or leaf may have acorresponding retention feature and the latch may capture and retain amovable mass and/or leaf via engagement of these retention features. Forexample, the moving mass and/or leaf and the latch may each havecorresponding notches or protrusions that engage when the latch istransitioned to the locked state. Other systems may rely upon apositional feature on the moving mass (e.g. a notch, detent, or peghole) to engage a pin, roller, etc. Still other latch variations maycomprise electromagnets, where a corresponding magnet or ferromagneticmaterial may be placed on the moving mass and/or leaf, where the latchelectromagnets may be used to capture and hold the moving mass and/orleaf such that the leaf is retained at the extremums. Some latchmechanisms may include a spiral voice coil. Other latches may functionas a brake, for example, a friction brake may be applied normal ororthogonal to the direction of leaf travel to stop and hold the leafusing frictional forces. Such brake-style systems may be configured toapply force at any desired location on the movable mass and/or leaf, anddoes not require precise alignment of a notch and detent, for example.The friction brake might be a pneumatic, electromagnetic,piezo-restrictive mechanism. Since a brake does not require precisealignment with a notch or protrusion at a certain location in themovable mass and/or leaf, there may be greater variability in theposition where the leaf is retained. This may allow the brake tomaintain the position of the leaf even when the various components ofthe spring-based drive mechanism are not precisely aligned, andtherefore may be able to tolerate any unexpected or unintentionalmechanical perturbations to the system.

One variation of a positional latch comprising an electromagnet (e.g., alatch in which engagement with the movable mass and/or leaf relies on apositional alignment between the latch and the movable mass and/or leaf)is depicted in FIGS. 8A-C. Such latch mechanism may be used with any ofthe collimator leaf drive mechanisms described herein. As shown in FIG.8A, a latch mechanism 800 may comprise an electromagnet 802 and acontrol arm 804 that selectively engages a portion of a leaf 806 bypivoting downward to engage a portion of the leaf 806 when the leafmoves into the control arm (e.g., an extremum). The downward motion ofthe control arm may be caused by leaf motion and contact, energizing ofthe electromagnet, or a combination of both. The electromagnet mayremain energized so as to retain the control arm in this downward,latched configuration, and de-energized or reverse energized (e.g., tohave a polarity that repels the control arm) to release the leaf. Afirst end 808 of the arm 804 may have a leaf engagement structure 810that corresponds to a catch or an engagement structure 812 on the leaf806, and the second end 816 of the control arm 804 may comprise amagnetic material. For example, the leaf engagement structure 810 may bea hook and the catch 812 may be a groove or ledge sized and shaped to beengaged by the hook. In some variations, the catch may include a rollerwhich may help to facilitate release of the leaf. The shape (e.g.,slope, extent, or curvature) of the catch surface may be adjusted tomake it easier or harder to release the roller. The portion of the leaf806 that has the catch 812 may be any structure that moves in concertwith the leaf, for example, the radiation-blocking portion of the leaf,or the support structures associated with the leaf. The latch mechanism800 may have three configurations, each of which are depicted in FIGS.8A-C. FIG. 8A depicts the latch mechanism 800 in the open configurationas a portion of the leaf 806 moves to the right. In this configuration,the polarity of the electromagnet 802 may be such that it repels aferromagnetic plate 818 on the second end 816 of the control arm 804,which may help to keep the first end of the arm 808 in an upward orhigher position. In FIG. 8B, the leaf portion 806 contacts the controlarm 804, which may cause it to rotate around the pivot point 817. Thismay cause a catch on the first end 808 of the control arm 804 to dropdown, and a ferromagnetic plate 818 on the second end 816 of the controlarm to move upward. The polarity of the electromagnet 802 may be changedsuch that it attracts the ferromagnetic plate 818. In FIG. 8C, theelectromagnet 802 has captured the ferromagnetic plate 818, holding thecatch in the down position, capturing the leaf. To release the leaf, theelectromagnet 802 may be energized with an opposite polarity, expellingthe ferromagnetic plate 818 away from the electromagnet 802 and pivotingthe control arm 804 such that the first end 808 is raised, therebyreleasing the leaf 806.

Some variations of a latch or actuator system of a collimator leaf drivemechanism may comprise a slotted link (e.g., scotch yoke) mechanism incombination with a rotary actuator or motor, which may be configured tolatch the leaf in both the open and closed positions. The yoke may beattached to the movable mass of the spring-based drive mechanism, and arotary actuator may be used to drive the pin in the yoke with aneccentric (by which the pin is offset by some radius from the axis ofthe rotary actuator). At the extremes of travel, the rotary actuator mayhave infinite mechanical advantage over the spring system, so no forcewould be required to hold the moving mass at the extremum. Rotating theactuator may release the spring system. The rotary actuator may be usedto add energy to the system by applying force in the direction of motionas the leaf transitions from one extremum to the other (e.g., betweenopen and closed positions). For example, the rotary actuator may be usedto add energy to the spring system if it is capable of moving the pinfaster than the spring system can move the yoke. The pin may then applyan accelerating force to the spring mass. As with a linear voice-coillatch mechanism, the rotary actuator may be operated at the resonantfrequency of the spring system to start the system from a de-energizedstate. Some variations may comprise a rotary solenoid with a 180 degreerange of motion, while other variations may comprise a brushless DCmotor with a range of motion that is more than 180 degrees. The shape ofthe slot within the scotch yoke may be adjusted to better match themotion of the spring system to the actuator characteristics, or to helpfine-tune the latch and release characteristics of the system or toadjust the mechanical advantage of the actuator as a function of throwand/or to better match actuator torque with the desired speedcharacteristics. For example, a shortened slot that does not allow theactuator to reach a full 180 degree rotation may bias the system towardsthe unlatched configuration (e.g., where the leaf is able to be moved bythe spring system). Alternatively or additionally, a small detent in theshape of the slot may bias the system towards the latched configuration(e.g., where the leaf is not movable by the spring system). Slotsurfaces that are curved or otherwise not perfectly vertical may be usedto accommodate rotary motions that are not at a constant velocity. Insome variations, this may be useful to help facilitate latching the leafin a closed or open position, since the rotary actuator will need toaccelerate and decelerate to enable latching at the extremums. In somevariations, the rotary actuator may be a rotary solenoid, since thelatch may not require a full 360 degree rotation. In some variations,the actuator may be biased towards release (thus requiring a smallholding torque to latch in position) by reducing the range of motion toslightly below a full 180 degrees.

One variation of a collimator leaf drive mechanism of a multi-leafcollimator that may be disposed in the beam path of a radiation sourcemay comprise a spring system (such as a spring resonator, including butnot limited to, any of the spring resonators described above) and anactuator system that includes a scotch yoke that selectively retains theleaf in either the open or closed position. The actuator system maycomprise a leaf shaft having a slot, a motor, a roller disposed withinthe slot, and a crank that couples the motor and the roller such thatactivation of the motor causes the roller to rotate with the slot. Thespring system may have one or more springs disposed along the leaf shaftwhich may provide a longitudinal force along the axis of the leaf shaftto move the leaf between a first location and a second location. Thefirst location may be an open position (or a closed position) while thesecond location may be a closed position (or an open position). Thespring system may provide the motive force for translating the leafbetween the first and second locations, while the actuator system mayselectively retain the leaf in the first location and the secondlocation. Optionally, the actuator system may also add energy to thespring system to compensate for the energy lost due to frictional forcesand/or to provide sufficient energy to the spring system to acceleratethe spring motion from a non-moving state to a desired target speed sothat enough kinetic energy is provided to transition the leaf betweenthe first and second locations. For example, the actuator system may addpotential energy into the spring system by compressing the spring(s)while retaining the leaf in either the first location or the secondlocation. The potential energy may be translated into kinetic energythat is sufficient to transition the leaf from one location to another.Whether spring forces or the actuator forces dominate the motion of theleaf may depend on the location of the roller within the slot, alongwith the geometry of the slot (e.g., radius of curvature, length andlocation of curved or straight regions, etc.), as described in theexamples below.

FIGS. 11A-11F depict one example of a collimator leaf drive mechanismcomprising a spring system and an actuator system that includes aslotted-link or scotch yoke mechanism. The location and movement of acollimator leaf 1102 (which is represented by a rectangular block) maybe driven by a spring system comprising a first spring 1106 a and asecond spring 1106 b located along a leaf shaft 1104 and an actuatorsystem comprising a slotted link mechanism (e.g., scotch yoke 1111) anda motor 1108. The sum of the translational forces (i.e., that move theshaft longitudinally as indicated by arrow 1101 in FIG. 11A) applied bythe spring system and the actuator system may move the leaf 1102 betweena first location 1150 and a second location 1160, and retain the leaf ateither of those locations as may be desired. In the first location 1150(which is depicted in FIG. 11A), the leaf 1102 may substantially orentirely obstruct a radiation path that is represented by the boundaries1151, 1161, and in the second location 1160 (which is depicted in FIG.11E), the leaf 1102 may not obstruct the radiation path. FIG. 11Cdepicts an intermediate configuration as the leaf 1102 moves from thefirst location 1150 (a leaf closed configuration) to the second location1160 (a leaf open configuration). The scotch yoke 1111 may be attachedto the leaf shaft 1104 and may comprise a slot 1110 located on a platethat is fixedly attached to the leaf shaft 1104, a roller 1112 disposedwithin the slot 1110 and a motor 1108 that rotatably translates theroller within the slot 1110. Depending on the location of the roller1112 within the slot 1110, the spring system forces may cause the leaf1102 to translate between the first and second locations, or theactuator system may oppose the spring forces and retain the leaf ateither the first location 1150 or the second location 1160, as may bedesirable. As depicted in FIG. 11A, the leaf shaft 1104 may be slidablyretained by two shaft mounting blocks 1120 a, 1120 b. The shaft mountingblocks 1120 a, 1120 b, may each have a lumen therethrough, and theblocks may be fixably mounted on a base 1121 such that the lumens of themounting blocks are aligned and the leaf shaft 1104 may extend throughthe lumens. The first and second springs 1106 a, 1106 b may be mountedto the leaf shaft 1104 between the shaft mounting blocks 1120 a, 1120 band the first and second spring blocks 1122 a, 1122 b, respectively. Thefirst and second spring blocks 1122 a, 1122 b may be fixedly attached tothe leaf shaft 1104. In this variation, where the springs 1106 a, 1106 bare used in compression, the ends of the springs may not be attached toeither the shaft mounting blocks or the spring blocks. In somevariations, one of the ends of the springs may be attached to the springblock (or shaft mounting block), while the other end of the springs maybe free from attachment. In other variations, where the springs may beused in tension, both ends of both of the springs 1106 a, 1106 b may beattached to the spring block and the shaft mounting block. For example,one end of the first spring 1106 a may be attached the first springblock 1122 a and the opposite end of the first spring 1106 a may beattached to the first mounting block 1120 a. The second spring 1106 bmay be similarly attached to the leaf shaft. While the spring blocks1122 are depicted as rings that circumscribe the leaf shaft, it shouldbe understood that spring blocks may have any other shape that may ormay not at least partially circumscribe the leaf shaft. For example, aspring block may be a protrusion on the shaft to which the springs maybe attached, and/or the springs may be welded, soldered, and/or adheredto the leaf shaft without any additional mount structure. The springs1106 are depicted as coil-shaped springs that circumscribe the leafshaft 1104, but it should be understood that in other types of springsmay be included, such as torsion bars, torsion springs, compressionsprings, etc., which may or may not circumscribe the leaf shaft.

FIGS. 11B, 11D and 11F are close-up depictions of the position of thescotch yoke mechanism when the leaf 1102 is retained in the closedconfiguration (i.e., at the first location 1150), in transit from theclosed configuration to the open configuration, and retained in the openconfiguration (i.e., at the second location 1160), respectively. Themotor 1108 of the actuator system is coupled to the roller 1112 by amotor shaft 1124 and a crank 1126, such that rotation of the crankrotates the roller 1112 within the slot 1110. FIG. 12A is a perspectivecomponent view of the coupling between the roller 1112, the crank 1126,and the distal-most end of the motor shaft 1124, FIG. 12B is a partialexploded view of the roller, crank and motor shaft of FIG. 12A, and FIG.12C is a cross-sectional view of the coupling between the roller, crankand motor shaft of FIG. 12A. In the variation depicted in FIGS. 11A-11F,the motor 1108 rotates the crank 1126 in a clockwise direction totransition the leaf from the closed configuration to the openconfiguration. The slot 1110 may have one or more curved regions toallow the leaf to move and transition between the first and secondlocations, as well as to retain the leaf at either of these locations,as desired. For example, the slot 1110 may have a first stop region 1128and a second stop region 1130. When the roller 1112 is located at eitherof these regions, the spring forces from the spring system along thelateral direction (indicated by arrow 1101) are opposed by the rolleragainst the stop regions 1129, 1130 in the slot. This may prevent thespring forces from laterally moving the leaf shaft, thereby retainingthe leaf at either the first or second locations, which may removekinetic energy from the system. That is, when the roller 1112 is locatedat the first stop region 1128, the first spring 1106 a may be compressedand/or the second spring 1106 b may be extended such that potentialenergy is added to the spring system that is at least equal to (and mayoptionally be greater than) the spring forces that were lost (e.g., dueto friction, etc.) during the motion of the springs and the leaf shaft.Similarly, when the roller 1112 is located at the second stop region1130, the second spring 1106 b may be compressed and/or the first spring1106 a may be extended such that potential energy is added to the springsystem that is at least equal to (and may optionally be greater than)the spring forces that were lost during the motion of the springs andthe leaf shaft. The radius of curvature and/or the angular sweep of thefirst stop region 1128 and the second stop region 1130 may be selectedsuch that the roller 1112 may traverse the curve(s) in that region whilestill providing a sufficient opposition force to the spring systemforces to retain the leaf in either the first location or the secondlocation.

One variation of a slot shape that may be used in a slotted link orscotch yoke mechanism is depicted in FIGS. 13A and 13B. FIG. 13A depictsa slotted plate 1300 that may be attached to a leaf shaft within which aroller may translate as part of a scotch yoke mechanism (for example, asdepicted and described above in FIGS. 11A-11F). The slotted plate 1300may have a slot 1302 with one of more curves that have different radiiof curvature. For example, one side of the slot 1302 may have curvedsegments with four different radii of curvature. In the variationdepicted in FIGS. 13A-B, the slot may be bilaterally symmetric along avertical axis of symmetry 1303 with the same curved segments on theopposite side of the axis of symmetry. A first segment 1304 a may have aradius of curvature of about 5 mm (e.g., 5.05 mm), a second segment 1304b contiguous with the first segment may have a radius of curvature ofabout 15 mm (e.g., about 15.3 mm), a third segment 1304 c contiguouswith the second segment may have a radius of curvature of about 6 mm(e.g., about 6.5 mm), and a fourth segment 1304 d contiguous with thethird segment may have a radius of curvature of about 5 mm (e.g., about5.05 mm). In this variation, when the roller is located in the first andsecond segments, the motion of the leaf is dominated by the forcesapplied by the spring system, and the leaf may move to translate betweenthe closed configuration and the open configuration (e.g., the firstlocation and the second location). When the roller is located in thethird and fourth segments, the leaf is held stationary in either theclosed configuration or the open configuration. As the roller translateswithin the slot in a counterclockwise direction and moves from the firstsegment 1304 a to the fifth segment 1305 a on the other side of the axisof symmetry 1303, the motor to which the roller is coupled may introduceadditional rotation energy to the roller to compensate for energy losses(e.g., mechanical energy losses) due to friction. The slot may comprisea sixth segment 1305 b, a seventh segment 1305 c, and an eighth segment1305 d that may be similar to (e.g., mirror-symmetric) to the secondsegment 1304 b, third segment 1304 c, and fourth segment 1304 d,respectively. The curvature of the first segment 1304 a and thecurvature of the fifth segment 1305 a may be selected such that theroller can smoothly translate between the two sides of the slot, and/ormay reduce the likelihood that the roller loses contact with the edgesof the slot as it translates between the first and fifth segments. Insome variations, the curvature of the first segment and the curvature ofthe fifth segment are such that they facilitate the movement of a rollerfrom one side of the slot to the other, so that even if the roller losescontact with the edge of the slot, the distance travelled by the rollerwhile it is not in contact with the slot is relatively short as comparedto the overall distance travelled by the roller. FIG. 13B is a depictionof the various curves of a slot 1310 (which may be the same as, orsimilar to, the slot 1302), where the various curves may correspond todifferent modes of operation. The slot 1310 may be bilaterally symmetricabout a vertical axis of symmetry, and one side of the slot may have afirst curved region 1312 a, a second curved region 1312 b continuouswith the first curved region, and a third curved region 1312 ccontiguous with the second curved region. There may be similarcorresponding curves on the opposite side of the slot 1310: a fourthcurved region 1314 a that corresponds with the first curved region 1312a, a fifth curved region 1314 b that corresponds with the second curvedregion 1312 b, and a sixth curved region 1314 c that corresponds withthe third curved region 1312 c. The descriptions of the first, secondand third curved regions below may apply to the fourth, fifth, and sixthcurved regions. Although each side of the slot in this example has threecurved regions, it should be understood that there may be any number ofcurved regions as may be desirable. Each of the curved regions may havecurves of varying radii of curvature, or may have curves with a singleradius of curvature. In variations where there may be multiple curveswith multiple radii of curvature, the transition from one curve to thenext may be continuous and smooth such that there are no abrupt,discontinuous or acute changes in the curvature. In some variations, thecurvature of these regions may be shaped such that the roller maintainssmooth contact with the edge of the slot. In variations where the rollermay lift away from the edge of the slot (e.g., moves away from the edgeof the slot), the curvature(s) may be shaped to promote a smoothtransition as the roller comes back into contact with the edge of theslot. Curves that facilitate smooth transition(s) roller may help tolimit the sound intensity as the roller comes back into contact with theslot edge. In particular, a roller may be most susceptible lifting awayfrom the slot edge as it translates between the first curved region 1312a and the fourth curved region 1314 a, at a top portion 1313 of the slot1310. The top portion 1313 of the slot may comprise at least a portionof the first and fourth curved regions, which may connect to each otherat an apex 1315. The top portion 1313 may have a curvature thatfacilitates smooth movement of the roller between the first curvedregion 1312 a and fourth curved region 1314 a, regardless of whether theroller maintains constant contact with the slot edge or lifts away fromthe slot edge as it moves in this region of the slot. In somevariations, as the roller moves within the top portion 1313, the motorto which the roller is attached may add energy back into the system tocompensate for various energy losses (e.g., mechanical losses such asfriction). For example, the system is configured to introduce additionalrotational energy to the roller as it moves across the apex 1315. When aroller of a scotch yoke or slotted link mechanism is located in the topportion 1313, the leaf may be in transit from one configuration toanother (from open to closed, or closed to open), and may be moving at aspeed such that this configurational change occurs within less thanabout 10 ms (e.g., less than about 6 ms, or less than about 4 ms). Thespring system may provide sufficient motive force in this mode ofoperation. The actuator system may optionally provide additional motiveforce that constructively adds with the spring force. In somevariations, the speed of movement may peak at the juncture between thefirst region 1312 a and the fourth 1314 a region (e.g., at the apex1315), though in other variations, the speed of movement may besubstantially the same as the roller moves within the top portion 1313.When the roller moves to the second curved region 1312 b, the actuatorsystem may provide a force that opposes the spring force sufficient toretain the leaf in either the open configuration (if the slot 1310 isused with the system depicted in FIGS. 11A-11F) or the closedconfiguration (if the slot 1310 is used in a system that has an oppositeorientation to the system depicted in FIGS. 11A-11F). Rotationallytranslating the roller in the second curved region 1312 b may not resultin a corresponding lateral movement of the leaf and/or leaf shaft. Thismay provide a margin within which the motor of the actuator system canaccelerate to the desired rotational speed with little or no lateralmovement of the leaf. If the roller moves to the third curved region1312 c, the actuator system may further compress a first spring of thespring system and/or expand a second spring of the spring system,converting kinetic energy in the actuator system to potential energy inthe spring system, thereby ensuring that the leaf is retained in eitherthe open or closed configuration. In some variations, when the roller isstopped within this third curved region 1312 c, a trailing edge of theleaf may be located further away from the boundary of the radiation beampath (in the case where the leaf is retained in the open configuration)or the trailing edge of the leaf may be located closer to the boundaryof the radiation beam path (in the case where the leaf is retained inthe closed configuration). As an example, arrow 1320 represents themovement of a roller within the slot as a leaf arranged as in FIGS.11A-11E is transitioned from an open configuration to a closedconfiguration, and arrow 1322 represents the movement of the same rolleras the leaf is transitioned from a closed configuration to an openconfiguration.

Other slot shapes and geometries may be used in a slotted-link or scotchyoke mechanism. FIG. 14A depicts a slot 1400 having a top portion 1402that has two straight segments that are parallel to each other connectedwith a curve with a constant radius of curvature and a bottom portion1404 having a partial oval shape comprising arcs with varying radii ofcurvature. In the slot 1400, the bottom portion 1404 may be wider thanthe top portion 1402. The widened, variable radius of curvature region1404 may provide a stable region 1405 (e.g., the portion of the slotwhere the scotch yoke mechanism supplies sufficient force to oppose thespring forces to retain the leaf in an open or closed configuration)that has an angular sweep of δ, which may be from about 5 degrees toabout 20 degrees. The value of δ may be determined at least in part bythe precision with which the motor that drives the roller 1406 canposition the roller at a desired location in the slot. That is, thesweep angle δ may provide a margin of tolerance for the motor drivingthe roller. The path of the roller is represented by dotted lines 1408and may be attained by a motor rotating the crank (not depicted here,but similar to the depiction in FIGS. 12A-12C) along the dotted lines1410. The path 1410 in the stable region 1405 may be an arc that maymatch or approximate the radius r of the crank. The stable region mayextend below the horizontal axis (i.e., |θ|>90°) in some variations. Thestable region may be symmetric about a horizontal axis 1407, which mayhelp to reduce the tendency of the roller to lose contact with the slotas it moves within the curvature of the slot.

While the slot shape and geometry may have multiple curves with variousradii of curvature, in some variations, the slot may have two straightparallel edges with two end curves with the same radius of curvature(so-called a straight slot). The stable region of a straight slot may bevery short, and therefore, unstable, as a slight rotation orperturbation of the roller in either direction of the stable region willallow the spring system to cause translation of the leaf. As such, thestable region of a straight slot may be considered a “singularitypoint”, since there is little or no margin of tolerance for a motordriving the roller such that any deviation from the “singularity point”allows the spring system to translate the leaf. One example is depictedin FIG. 14B. A scotch yoke or slotted link mechanism comprising astraight slot 1420 may optionally comprise a spring 1422 located withinthe bottom curve 1424. The spring 1422 may be a coil spring (as depictedin FIG. 14B), or any other type of spring. The spring 1422 may be sizedso that its positive angular stiffness imparted to the crank (notdepicted here, but similar to the depiction in FIGS. 12A-12C) maycounteract the negative angular stiffness in the scotch yoke when loadedby the spring system at the singularity point. The spring load of thespring system may create an angular stiffness at θ=±90°. The spring 1422may engage with positive stiffness for |θ|>90°.

FIGS. 15A-15D depict another variation of a collimator leaf drivemechanism comprising a spring system and an actuator system including ascotch yoke or slotted link mechanism. While the variation of FIGS.11A-11E comprises a spring system having coil springs located along theaxis of motion of the leaf, the variation of FIGS. 15A-15D comprises aspring system having a torsion spring disposed orthogonal orperpendicular to the axis of motion of the leaf. As exemplified in thesetwo examples, the type(s) and location(s) of the springs of the springsystem may vary as desired. Some leaf drive mechanisms may comprise aspring system where the one or more springs are co-linear and/orco-planar with the travel path of the leaf while other drive mechanismsmay comprise a spring system where the one or more springs are notco-linear or co-planar with the travel path of the leaf. The particulararrangement, location, and/or spring type(s) may be determined at leastin part by the size and space on a gantry of a radiation therapy systemthat is available to the collimator, as well as the number, shape, andsize of the collimator leaves. Turning now to the example depicted inFIG. 15A, the drive mechanism 1500 may comprise a frame 1504 to which aleaf 1502 is attached, the frame 1504 pivotably attached to a springsystem comprising a torsion spring 1506. The frame 1504 may comprise arail 1505 disposed along a top edge of the frame, extending generallybetween the leaf 1502 and the attachment location for the spring system.The rotatable joint or pivot 1505 may convert the rotational, twistingmotion of the torsion spring 1506 to a lateral, longitudinal motion ofthe frame 1504 (in direction of arrow 1503), which in turn act to movethe leaf 1502 between the open and closed configurations. The torsionspring 1506 is located such that it is orthogonal to the longitudinalmotion of the frame (as indicated by arrow 1503). The drive mechanism1500 may comprise an actuator system comprising a scotch yoke, where theslotted portion 1510 of the scotch yoke is fixedly attached to the frame1504, and a roller 1512 is disposed within the slot 1510. The roller1512 may rotatably translate within the slot 1510 by way of a crank 1526coupled to a motor 1508 via a motor shaft 1524. In some variations,there may be a first bearing 1525 a and a second bearing 1525 b locatedalong the length of the shaft to support and retain the shaft 1524.Although the shape of the slot 1510 depicted in FIGS. 15A-15B resemblesthe shape of a straight slot, it should be understood that the slot mayhave any of the shapes described and depicted previously (i.e., may haveone or more curved regions that may have varying radii of curvature andangular sweeps, one or more spring stops, etc.). FIG. 15C depicts onearrangement of a plurality of leaf drive mechanisms of FIGS. 15A-15B fora plurality of leaves in a multi-leaf collimator. FIG. 15C depicts thearrangement of 32 leaves with their corresponding 32 drive mechanisms.The drive mechanisms may be interleaved, staggered, etc. to attain thedesired leaf-to-leaf spacing in the collimator. Drive mechanisms andleaves may be assembled in a particular order to attain the depictedarrangement. An illustrative example of an assembly method forassembling eight drive mechanism units (where each unit is similar tothe drive mechanism 1500 depicted in FIGS. 15A-15B) for a collimator isdescribed below and depicted in FIGS. 15C-15H. The method may be used toassemble the eight drive mechanism units (each unit comprising a leaf)1541, 1542, 1543, 1544, 1545, 1546, 1547, 1548 that are schematicallydepicted in FIG. 15C. This method may be repeated as many times asdesired in order to assemble a collimator with the desired number ofleaves (e.g., for a 16 leaf collimator, 32 leaf collimator, 64 leafcollimator, etc.). A collimator may comprise a top plate 1530, a middleplate 1532 and a bottom plate 1534. Various components of each of theeight leaf drive mechanisms may be supported and retained by one or moreof these plates, as depicted in FIG. 15D. For the purposes of theassembly method described and depicted in FIG. 15F, each of the leafdrive mechanisms or units comprise a chassis assembly, a scotch yokeassembly, an actuator shaft assembly. As an example, the chassisassembly may comprise the frame 1504, leaf 1502 and rail 1505, thescotch yoke assembly may comprise the roller 1512 and crank 1526, theactuator shaft assembly may comprise the actuator shaft 1524 and thefirst and second bearings 1525 a, 1525 b. The actuator shaft assemblymay be coupled to the motor 1508. FIGS. 15E-15G depict one variation ofan assembly method 1550 for assembling eight leaf drive units. Arrangingthe leaf drive units, and moving the various assemblies of each driveunit to create space to accommodate an adjacent drive unit may help topack the individual units closely to their adjacent units so that theoverall footprint of the collimator may be reduced, and the leaves maytile closely to each other in the radiation beam path. FIG. 15H depicts32 leaves with each of their corresponding drive mechanisms of a 64 leafcollimator. The 32 leaves and their corresponding drive mechanisms maybe assembled by repeating the method depicted in FIGS. 15E-15G fourtimes.

While the spring-based leaf drive mechanisms described above areconfigured to move the leaf only when a transition between the open andclosed positions is desired, in other spring-based drive mechanisms, thesprings may continuously move the spring between the open and closedpositions. The timing of when the leaf is in the open position or closedposition may be synchronized with respect to a pulsing radiation source.For example, to block the transmission of radiation from a radiationsource pulsing at a selected frequency, the springs may oscillate suchthat when the radiation source pulses a radiation beam the leaf is inthe closed position. To permit the transmission of radiation, theoscillation of the springs may be phase shifted with respect to itsprevious oscillatory state so that when the radiation source pulses aradiation beam, the leaf is in the open position. FIGS. 9A and 9B depictplots of the position of a leaf driven by a continuously oscillating orresonating spring-based drive mechanism as a function of time. Timepoints 900, 902, 904 represent time points at which a radiation sourcepulses a radiation beam. FIG. 9A depicts the position of a leaf that isdriven by a spring that oscillates in-phase with the pulsing of theradiation source, so that the leaf is in the closed orradiation-blocking position when the radiation beam is emitted. Theoscillation is such that when the leaf is moved to the open position,the radiation source is not emitting any radiation, so no radiation beamis transmitted to the tissue even though the leaf is not in the closedposition. FIG. 9B depicts the position of a leaf that is driven by aspring that oscillates out-of-phase with the pulsing of the radiationsource, so that the leaf is in the open or radiation-transmittingposition when the radiation beam is emitted. The oscillation of the leafdepicted in FIG. 9B is 180 degrees out-of-phase from the oscillationdepicted in FIG. 9A.

If it is desired that the leaf remains closed during the radiationpulse, or remains open during the radiation pulse, the spring mayoscillate according to the trajectory of either FIG. 9A or 9B. Totransition the leaf from being closed to being open (or vice versa)during the radiation pulse, the timing of the oscillating needs to beshifted. The phase shifting of the spring oscillation from beingin-phase with the radiation pulses to being out-of-phase with theradiation pulses (and vice versa) may be achieved by temporarilyincreasing or decreasing the frequency of the spring oscillation. Insome variations, an actuator coupled to the spring and/or leaf may applya force to the spring and/or leaf to alter the motion of the springand/or leaf. FIGS. 9C and 9D depict two ways in which the phase of thespring oscillation may be shifted so that the leaf transitions frombeing in the closed or radiation-blocking position during a radiationpulse (e.g., during time points 906, 908) to being in the open orradiation-transmitting position during the radiation pulse (e.g., duringtime points 910, 912). In FIG. 9C, the oscillation is shifted from beingin-phase with the radiation pulse to being 180 degrees out-of-phase withthe radiation pulse by temporarily increasing the frequency of theoscillation. As the leaf moves towards the open position, it is “kicked”back towards the closed position. In FIG. 9D, the oscillation is shiftedfrom being in-phase with the radiation pulse to being 180 degreesout-of-phase with the radiation pulse by temporarily decreasing thefrequency of the oscillation. The leaf is slowed down as it movestowards the open position so that it reaches the open position at timepoint 910.

FIGS. 9E and 9F depict one variation of a continuously-oscillating,spring-based leaf drive mechanism comprising one or more actuators forshifting the phase of the oscillation as described above. A leafassembly may comprise a leaf 920 and support 922. The leaf drivemechanism may comprise a first spring 924 that may be the primary motiveforce for moving the leaf assembly between the open and closedpositions. The first spring 924 may be continuously oscillating inaccordance with the position-time plots depicted in FIGS. 9A-9B. Anactuator 926, such as a voice coil driver, may be coupled to the leafassembly in order to push and/or pull the leaf assembly to compensatefor any spring energy lost due to friction, as well as to start the leafmoving from a stationary state (e.g., when the collimator powers up atstart up, or when the system has been reset after a movement error isdetected). The voice coil actuator 926 may be attached to the leafsupport 922. The spring-based drive mechanism may also comprise a secondspring 928 that may have a disengaged configuration and an engagedconfiguration. The configuration of the second spring 928 may becontrolled by a solenoid 930. FIG. 9E depicts the second spring 928 inthe disengaged configuration, where the second spring is not in thetravel path of the leaf assembly and does not affect the movement of theleaf assembly by the first spring 924. When the second spring 928 is inthe disengaged configuration, the leaf assembly may oscillate accordingto the movement of the first spring 924, according to the position-timeplot of either FIG. 9A or FIG. 9B. When it is desired to shift the phaseof the oscillation of the first spring 924, the solenoid 930 may beactivated to transition the second spring 928 to the engagedconfiguration, as depicted in FIG. 9F. In the engaged configuration, thesecond spring 928 can affect the motion of the leaf assembly in order toshift the phase of the oscillation. In some variations, the secondspring 928 may temporarily increase the frequency of the oscillation,similar to the effect depicted in FIG. 9C. Alternatively oradditionally, the second spring 928 may be configured to provide anadditive force to the oscillation of the first spring 924 to temporarilyincrease the frequency. In some variations, the second spring 928 may beremoved in order to temporarily reduce the frequency.

The position-time plot of another variation of a spring-based leaf drivemechanism is depicted in FIG. 9G. The oscillation of a spring thatdrives the movement of a leaf or leaf assembly between the open andclosed configurations may be adjusted such that the leaf “overshoots”the open and closed positions, and that the duration of time in whichthe leaf has “overshot” the open or closed position coincides with theradiation pulse width (radiation pulse interval 944). That is, the leafmay move past the nominal position where radiation is either transmittedor blocked, and the duration of time in which the leaf has moved pastthe nominal point is at least the duration of the radiation pulse width.This may help reduce the need to latch the spring at either the open orclosed positions. For example, if it is desired for the leaf totransition between the open position and the closed position for twoconsecutive radiation pulses (e.g., the leaf follows the 942trajectory), the leaf is not latched at the open position since the timethat the leaf spends overshooting the open position spans the durationof the radiation pulse. The leaf is then allowed to oscillate to theclosed position for the next radiation pulse. If however, if it isdesired for the leaf to remain in the open position for two consecutiveradiation pulses (e.g., the leaf follows the 940 trajectory), the leafposition may be secured by a latch. The latch has the entire duration ofthe radiation pulse interval 944 to engage the leaf in order to retainit in open position, and to prepare to release the leaf. In thisvariation, the latch has about 10 ms to engage and release the leaf.This is in contrast to other variations where the time interval duringwhich the latch must engage and release the leaf is much shorter, forexample, 2 ms or less. The time duration of the “overshoot” may beadjusted by varying the spring constant of the springs. For example,non-linear springs may be used to attain the desired timing parameters.While the above example describes latching the leaf at the openposition, it should be understood that similar principles apply tolatching the leaf at the closed position.

The timing between the firing of a radiation beam and the opening andclosing of individual leaves of a binary collimator may be adjusted toattain a desired pattern of beamlets. In some variations, the pattern ofbeamlets may form a contiguous, two-dimensional shape, which mayapproximate the shape and size of the region of interest (e.g., tumor).One method of controlling the collimator may comprise staggering thetiming of the opening of the collimator leaves such that when theradiation beam is fired, some leaves are open, others are closed, andstill others are transitioning between the open and closed states. Thetrailing edges of the leaves that transitioning between the open andclosed states (i.e., the portion of the leaves that are in the beampath) may approximate the edges of the desired beam shape. The relativetiming between firing the radiation beam and the position of aparticular leaf during beam firing may depend at least in part on thetime it takes for that leaf to transition between the open and closedstates, as well as the desired shape as a sum of all the beamlets. FIG.20A depicts an example of binary collimator leaves A-F, 1-4, that are invarious states of transitioning between an open and closed states inorder to form a pattern of beamlets. The timing of the opening of leavesA-F, 1-4 relative to the beam firing time t_(f) is depicted in thetiming diagram of FIG. 20B in order to attain the leaf positionsdepicted in FIG. 20A. For the purposes of this example, it is assumedthat all the leaves start in the closed state, the maximum width of abeamlet is 5 units and it takes 5 ms for a leaf to transition from theclosed state to the open state. Some beamlets may form a contiguousshape, while other beamlets may not be part of the contiguous shape, butmay be used to irradiate nearby tumor regions without irradiating (orreducing the irradiation of) tissue between the nearby tumor regions. Acontiguous shape 2000 may be formed by varying the timing of the openingof adjacent collimator leaves. Individual beamlets 2002, 2004, 2006 mayhave different beam widths depending on the relative timing betweentheir opening and the firing time t_(f). In the pattern of FIG. 20A,leaves 1-4 are entirely open at firing time t_(f) (i.e., the trailingedge of each leaf clears the entire beam width), and the time at whichleaves 1-4 begin to open is t₀. The remaining leaves A-F are in variousintermediate positions as they transition from the closed position tothe open position, and accordingly, each begins to open at varyingdelays from t₀. For example, leaf D is nearly entirely open at the timeof firing t_(f), and may start to open before leaf E. The width of thebeamlet associated with leaf A is smaller than the width of the beamletassociated with leaf B, therefore, the opening of leaf A is more delayedthan the opening of beam B relative to t₀. The desired beam profile maybe determined during a pretreatment phase, and may be based on images ofthe tumor acquired via one or more imaging modalities, including but notlimited to CT, MRI, PET, etc. A computer-implemented method may computethe relative timing of collimator leaf opening in order to attain thedesired radiation profile at the time of beam firing, based on thetransition time of the leaves between the open and closed positions andwhether the leaves start from an open position or a closed position. Itshould be understood that this method may be used with any of the binarycollimator leaf drive mechanisms described herein. Although the exampledepicted in FIGS. 20A and 20B assume that all of the leaves are in theclosed position at t₀, in other examples, the leaves may all be in theopen position, or some leaves may be open while other leaves may beclosed.

While some spring-based leaf drive mechanisms may use linear springs(i.e., springs that have a constant spring constant), other spring-basedleaf drive mechanisms may use non-linear springs (i.e., springs thathave a variable spring constant). The sinusoidal “position vs. time”trajectory (a.k.a. “shape”) associated with linear spring resonatorsystems may change when using one or more non-linear springs. Forexample, a “hardening” spring may cause the system to spend less timenear extrema, and a softening spring may increase the time spent nearextrema. The spring behavior may not be symmetric. In some variations,the springs for a spring-based leaf drive mechanism may be selected suchthat the leaf may have a shorter dwell time in the closed position and alonger dwell time in the open position. As described above with respectto the cam-based leaf drive mechanism, a spring-based leaf drivemechanism may comprise a single hard latch for the closed position. Theactuator used to restore energy to the spring system may optionally beused to tune the shape of the motion. When the actuator applies force inthe same direction as the spring, it can be used to “harden” the spring,and alternately when the actuator force is in the opposite direction,the overall behavior will be that of a “softened” spring.

Another variation of a leaf drive mechanism that may be used in ahigh-bandwidth multi-leaf collimator of a radiation therapy system(e.g., an emission guided radiation therapy system) may comprise a fluidpower mechanism, for example, a pneumatic cylinder or motor, or ahydraulic cylinder or motor. A collimator leaf may be coupled to themovement of the piston of a fluid power mechanism. In some variations, afluid power actuation mechanism may comprise a barrel, a piston movablewithin the barrel, a fluid source, and one or more fluid conduitsbetween the fluid source and the barrel. The piston may be coupled to acollimator leaf such that the piston motion causes a linear motion ofthe leaf. The travel path of the leaf may be substantially aligned,and/or co-linear with, and/or parallel with, the longitudinal axis ofthe barrel. The one or more fluid conduits may comprise one or morevalves to regulate and control the fluid flow into the barrel. The oneor more valves may be independently operable and controlled such thateach valve may open or close separately from the other valves. Acontroller may be configured to coordinate the timing of the opening andclosing of various valves with respect to each other to attain thedesired leaf motion within the time frames specified previously.Alternatively, the fluid flow into the barrel may be controlled by asingle valve. While the examples described herein may be directed to apneumatic cylinder or motor, it should be understood that similaroperating principles may also apply to a hydraulic cylinder or motor.

One variation of an actuator system comprising a pneumatic mechanismthat may be included in a collimator for a radiation therapy system isdepicted in FIGS. 10A-10G. A pneumatic leaf actuation mechanism 1000 maycomprise a barrel 1002, a piston 1004 movable along the length of thebarrel, a first valve 1006 that is fluidly connected to the barrel via avalve conduit 1016 and located at a distal portion of the barrel, asecond valve 1008 that is fluidly connected to the barrel via a valveconduit 1018 and located at a proximal portion of the barrel, a fluidsource 1014 and fluid conduit 1012 a,b that connects the fluid source1014 to each of the first and second valves. A leaf 1010 may beconnected to a piston rod 1005 such that movement of the piston withinthe barrel 1002 moves the leaf between open and closed positions. Inthis variation, the leaf travel path is substantially aligned with thelongitudinal axis of the barrel. The location where the proximal valveconduit 1018 connects to the barrel may be such that it is locatedproximal to the piston seal 1003 regardless of the position of thepiston 1004, and the location of the distal valve conduit 1016 connectsto the barrel may be such that it located distal to the piston seal 1003regardless of the position of the piston 1004. Each of the first andsecond valves 1006, 1008 may each comprise two source ports and oneoutput port. The output ports 1020 a,b may connect to the valve conduits1016, 1018 respectively. The first source ports 1022 a,b may be fluidlyconnected to a pressurized fluid source (e.g., air pressurized at 120psi) via fluid conduits 1012 a,b. The second source ports 1024 a,b maybe connected to air at atmospheric pressure (i.e., vented). In somevariations, the second source ports may be air vents. The source ports1022 a,b and 1024 a,b of each of the first and second valves 1006, 1008may be individually opened or closed to connect the output port 1020 a,bto either pressurized air or atmospheric air. Each valve may becontrolled such that the first and second source ports for that valveare not both open at the same time; either the first source port is openor the second source port is open, but not both. For the purposes of thedescription below, a valve will be described as “on” when the outputport is connected to the pressurized (e.g., high pressure) air sourceand will be described as “off” when the output port is connected to airat atmospheric pressure (e.g., vented). In some variations, beforepressurized air is provided on one side of the piston seal 1003 (e.g.,either the proximal side or the distal side), atmospheric air may beprovided to the other side of the piston seal 1003. This may help toincrease the speed with which the pressurized air can move the pistonfrom one side of the barrel to the other. Venting the air in this mannermay help reduce the time it takes for a leaf to transition between theclosed and open positions.

FIGS. 10B-10F schematically depict the sequence of events as a pneumaticactuation mechanism transitions a leaf from the closed position to theopen position and back to the closed position. FIG. 10G depicts timingdiagrams of the activation of the first and second valves (i.e., turningon and/or turning off) with respect to the position of the leaf, wherethe leaf transitions from the closed position before time point 1030 tothe open position at time point 1036 and back to the closed position attime point 1042. While the time interval between time points 1030 and1036 is 10 ms, it should be understood that the interval may be anylength of time. Similarly, although the time that the leaf is in theopen position (i.e., the interval between time points 1036 and 1040) orin the closed position (i.e., the interval between time points 1042 and1046) is depicted to be 6 ms, it should be understood that the leaf openor closed duration may be any desired length of time. More generally,the different time intervals shown in the timing diagram of FIG. 10G mayvary depending on the desired speed of the leaf transitions and the timeat which a leaf needs to be in the open or closed position.

FIG. 10B depicts the leaf 1010 in the closed position. In that position,the first valve 1006 may be connected to atmospheric pressure air (i.e.,vented), while the second valve 1008 may be connected to the highpressure air source 1014 (i.e., second source port 1024 a of first valveopen, first source port 1022 b of the second valve open). In thisexample, in order to move the leaf from the closed position to the openposition by time point 1036, the first and second valves initiate thetransition starting at time point 1030 (which is, in this case, 10 msprior to the time that the leaf is in the open position). At time point1030, the second valve 1008 is turned off and at time point 1032, thefirst valve 1006 is turned on. During the time interval I1 between timepoints 1030 and 1032, the pneumatic actuation mechanism in thepre-opened state, which is depicted in FIG. 10C. The duration ofinterval I1 may be about 2 ms. After the first valve 1006 is turned on,air that has been transferred from the high pressure source 1014 to thebarrel 1002 may start moving the piston at time point 1034 to urge theleaf towards the open position. The leaf may be moved to the openposition by time point 1036, and the interval I2 is the time it takesfor the leaf to transition from the closed position to the open position(which in this example, is 4 ms). FIG. 10D depicts the configuration ofthe pneumatic actuation mechanism at time point 1036, when the leaf isin the open position.

If it is desired to move the leaf 1010 back to the closed position inthe next phase (i.e., in the next firing position, this leaf needs to beclosed), then the first valve 1006 may be turned off at time point 1036.At time point 1038, the second valve 1008 may be turned on. During thetime interval I3 between time points 1036 and 1038, the pneumaticactuation mechanism in the pre-closed state, which is depicted in FIG.10E. The duration of interval I3 may be about 2 ms. After the secondvalve 1008 is turned on for a period of time, air that has beentransferred from the high pressure source 1014 to the barrel 1002 maystart moving the piston (and therefore, the leaf) at time point 1040towards the closed position. The leaf may be moved to the closedposition by time point 1042, and the interval I4 is the time it takesfor the leaf to transition from the closed position to the open position(which in this example, is 4 ms). The time it takes for the leaf totransition from the closed to open position (i.e., interval I2) may ormay not be the same as the time it takes for the leaf to transition fromthe open to closed position (i.e., interval I4).

If it is desired to move the leaf 1010 to the open position in the nextphase (i.e., in the next firing position, this leaf needs to be open),then the steps starting from time point 1030 may be repeated. That is,at time point 1042, the second valve 1008 may be turned off and then attime point 1044 the first valve 1006 is turned on. These steps may berepeated in accordance with commands from a controller to the valves tomove the leaf 1010 between the open and closed positions.

Alternatively or additionally, some variations of a fluid power systemmay comprise one or more bumpers located at the two extrema of the leaftravel path (e.g., at the open position and at the closed position)within the barrel. As the piston moves to either of the travel path, itmay contact the bumper(s). This may facilitate a slower/gradualdeceleration of the motion of the leaf as it arrives at the end of thetravel path. This may help to prolong the life of the piston and barrelmechanism, since excessive force and high repetition may damage thepiston and/or barrel without proper damping. In some variations, thebumper(s) may be located outside of the barrel, while in othervariations, the bumper(s) may be located inside of the barrel. Onevariation of a fluid power system comprising one or more bumpers isdepicted in FIG. 16H. As depicted there, the drive mechanism 1690 for aleaf 1691 may comprise a pneumatic actuator system having a barrel 1696,a piston 1692 having a seal 1694 longitudinally movable within thebarrel 1696, and a first bumper or damper 1698 located adjacent to afirst end wall of the barrel, and a second bumper or damper 1699 locatedadjacent to a second end wall of the barrel (e.g., that is opposite thefirst end wall). The pneumatic system may also comprise a first washeror disk 1693 disposed over one side (or end) of the shaft 1697 of thepiston 1692 and a second washer or disk 1695 disposed over the otherside (or end) of the piston shaft (e.g., adjacent to the leaf 1691). Thefirst and second washers or discs may be fixedly attached to the pistonshaft 1697, and in some variations, may be protrusions or curvesextending from the shaft 1697. As the piston 1692 translates withrespect to the barrel 1696, the first disk 1693 may contact the firstdamper 1698 when the leaf is in the closed position, and the second disk1695 may contact the second damper 1699 when the leaf is in the openposition. In variations where the dampers are located within the barreladjacent to the two end walls, the piston seal may contact the damperswhen the leaf moves to the closed position or the open position. Thehardness, thickness, and material(s) of the one or more dampers may beselected to absorb enough energy so that the leaf can come to arelatively gradual or gentle stop without being over-damped, and shouldnot be so firm or thick or non-compliant that the leaf bounces off thedamper (i.e., under-damped). That is, the material properties andgeometry of the dampers may be selected such that the force from theleaf impact is critically damped. In some variations, a damper maycomprise two layers made of two different materials. The firstleaf-contacting layer of the damper may be a harder material (e.g.having a higher durometer) than the second layer. This may help todistribute the impact force of the leaf over a larger area of the damperso that the energy at the local point of impact is dispersed as it isabsorbed. The first leaf-contacting layer may also be a tougher materialthan the material of the second layer so that it can sustain the wearand tear of repeated contact with the leaf. In some examples, the firstleaf-contacting layer of the damper may be made of a material having aShore A durometer of about 90, while the second layer may be made of amaterial having a Shore 00 durometer of about 70. In some variations,the total thickness of the damper may be about 0.5 in to about 2 in,e.g., about 0.68 in, about 0.75 in, etc. The thickness of the firstleaf-contacting layer may be from about 0.04 in to about 1 in, e.g.,about 0.0625 in, about 0.075 in, etc. The thickness of the second layermay be from about 0.4 in to about 1 in, e.g., about 0.625 in, about 0.5in, 0.75 in, etc.

The geometry of the barrel and the corresponding piston may be such thatthe pneumatic actuation mechanism is compactly arranged in aspace-efficient manner. For example, the cross-sectional shape of thebarrel and the piston may be non-circular. The cross-sectional shape maybe any shape that has a width that is relatively narrow as compared toits length, and may be, for example, rectangular or oval-shaped, asdepicted in FIGS. 10H-10I. Such narrow geometry may facilitatespace-efficient packing of the fluid power actuation mechanisms. Thefluid source may be a fluid compressor. The fluid source may be locatedon the gantry of a radiation therapy system, or may be located off thegantry.

One variation of a collimator leaf drive mechanism comprising a springsystem and a pneumatic actuator system that may be included in aradiation therapy system is depicted in FIGS. 16A-16F. The drivemechanism 1600 may comprise a pneumatic actuator system comprising abarrel 1602 with a longitudinal lumen 1603, a first side opening 1604, asecond side opening 1606, and a piston 1608 with a piston seal 1610 thatmay be movable within the barrel between the first and second sideopenings, and a spring system comprising a first spring 1612 disposed ona first side of the piston seal 1610 and a second spring 1614 disposedon a second side of the piston. The collimator leaf 1616 may be attachedto the piston 1608 via a leaf shaft 1618. In some variations, the leafshaft 1618 may be integral with the piston 1608, as depicted in FIG.16B. The spring system may be located within the barrel of the pneumaticsystem, or may be located outside of the barrel of the pneumatic system.For example, FIG. 16B depicts one example where the spring system (firstspring 1612 and second spring 1614) is located within the longitudinallumen of the barrel. The first spring 1612 may be disposed between thepiston seal and a first spring stop 1620 and the second spring 1614 maybe disposed between the piston seal and a second spring stop 1622, suchthat the first and second springs are on opposite sides of the pistonseal. The first and second spring stops 1620, 1622 may each have a lumenthrough which the piston 1608 may be slidably disposed. In otherexamples, the spring system may be located outside of the barrel of thepneumatic system, as depicted in FIG. 16F. In drive mechanism 1650, thefirst spring 1652 is disposed outside of the barrel 1656 between a firstspring mount or disk 1660 attached to the piston 1657 and a first springstop or disk 1664 attached to the barrel. The second spring 1654 isdisposed outside of the barrel 1656 between a second spring mount ordisk 1662 attached to the piston 1657 and a second spring stop or disk1666 attached to the barrel. Some variations may not have a spring stoplocated on either side of the barrel, but the springs may be disposedbetween the end walls of the barrel and the spring mounts. The piston1657 (and in turn, the first and second spring mounts 1660, 1662) iscapable of sliding within the first and second spring stops 1664, 1666such that the piston seal moves between the two openings in the barrel.Placement of the springs external to the barrel may help facilitaterepair and/or replacement of the springs so that repairs of the springsystem may be performed with little or no impact to (or disassembly of)the pneumatic actuation system. Alternatively or additionally, the drivemechanisms 1600, 1630, 1650 may comprise one or more bumpers or dampersas described and depicted in FIG. 16H.

The drive mechanisms 1600, 1630, 1650 may be operated in the samemanner, for example, as described above with respect to FIGS. 10B-10G.The first and second springs in drive mechanisms 1600, 1630, 1650 mayadd constructively with the force provided by the injected fluid toprovide a cumulative motive force that may move the piston seal withinthe barrel at a desired speed so that the transition between the openand closed configurations may occur within a desired time interval. Thefluid flow into and out of the barrel may also be adjusted such that themagnitude of the pressure provided by the fluid on one side of thepiston seal is at least equal to (and/or may exceed) the force appliedby the spring system on the opposite side of the piston seal, so thatthe leaf may be held in a first location or a second location (i.e., aclosed configuration or an open configuration). When the fluid pressureon one side of the piston seal opposes and exceeds the forces applied bythe spring system, the spring(s) of the spring system may be expandedand/or compressed (e.g., compressed on one side of the piston seal andexpanded on the opposite side of the piston seal) such that potentialenergy is added into the spring system. The addition of potential energyinto the spring system by the pneumatic actuator system may help tocompensate for the loss of energy as the leaf moves between the open andclosed configurations (e.g., due to friction). FIG. 16C depicts thedrive mechanism 1600 and the leaf 1616 in a closed configuration (whichmay correspond to the configurations described and depicted in FIGS. 10Band 10C). FIG. 16D depicts the drive mechanism 1600 and the leaf 1616 inan open configuration (which may correspond to the configurationsdescribed and depicted in FIGS. 10D and 10E). As described above withrespect to the configurations depicted in FIGS. 10C and 10E, beforepressurized air is provided on one side of the piston seal, atmosphericair may be provided to the other side of the piston seal. This may helpto increase the speed with which the pressurized air can move the pistonfrom one side of the barrel to the other. Venting the air in this mannermay help reduce the time it takes for a leaf to transition between theclosed and open positions. In some variations, pressurized air may beprovided to help decelerate the leaf at the end of the motion. Forexample, as the piston moves closer to the location depicted in FIG.10D, the second valve 1008 may be opened to connect to the pressurizedair source to reduce the speed of the piston 1004, which may prevent theleaf from traveling further than its desired endpoint, reducing the leafmotion settling time and preventing the spring from compressing beyondits design point. Similarly, as the piston moves closer to the locationdepicted in FIG. 10F, the first valve 1006 may be opened to connected tothe pressurized air source to reduce the speed of the piston. Using airpressure to facilitate deceleration may help to reduce the wear and tearon the piston, increase spring life, and decrease the settling time forthe leaf motion.

The first and second springs in leaf drive mechanism 1600 may have alength such that they are in contact with the piston seal for the fullstroke between the open and closed configurations. For example, a firstend of the first spring may be attached to the first spring stop and thesecond end may not be attached to the piston seal, but the length of thefirst spring is such that the second end is in contact with the pistonseal. Alternatively or additionally, the second end may be attached tothe piston seal. The second spring may have a similar arrangement. Insome variations, one spring is attached to the piston seal, while theother spring is not attached to the piston seal. In still othervariations, one or more of the springs may be attached to the pistonseal, but not attached to a spring stop on either end of the barrel. Inother variations, either or both the first and second springs may have ashortened length such that the spring(s) does not remain in contact withthe piston seal for the full stroke. For example, leaf drive mechanism1630 may have a spring system comprising a first spring 1632 and asecond spring 1634 located within a barrel 1636. One end of each of thefirst and second springs may be attached to corresponding spring stops1638, 1640. In the variation depicted in FIG. 16E, the other end of thesecond spring 1634 may not be attached to the piston seal 1637, and mayhave a length that is shorter than the distance between the first sideopening 1631 and barrel end wall 1633 such that the second spring 1634does not contact the piston seal 1637 as it moves toward the first sideopening 1631. The first spring 1632 may have a similar arrangement, ormay be attached to the piston seal 1637 and/or have a length that is atleast the same as the distance between the opposite barrel end wall 1635and the second opening 1641. The shorter spring(s) may allow the pistonseal to “fly” across center of travel while still being pushed by thefluid. This may cause the deceleration of the seal as the leafapproaches the open or closed position to start later. The arrangementdepicted in FIG. 16E may result in faster travel through the middle ofthe stroke (as compared to an arrangement where the springs are attachedat both ends to the piston seal and spring stops) but may also causesome “over-travel” at the end of the stroke (i.e., the leaf travelsbeyond the minimum distance to clear the radiation beam path in the openconfiguration, and/or the leaf travels beyond the minimum distance toobstruct the radiation beam path in the closed configuration).

FIG. 16G depicts an assembly of four leaf drive mechanisms, eachcomprising a pneumatic actuation system and a spring system as describedabove. The spring systems 1682 a, 1682 b, 1682 c, 1682 d of each of thefour drive mechanisms may comprise springs that are external to thebarrel of the pneumatic actuation mechanism. Each of the four leaves(not shown) may be coupled to the four drive mechanisms by four frames1684 a, 1684 b, 1684 c, and 1684 d. The drive mechanisms may be arrangedsuch that they are tiled together in a staggered fashion, so that thedrive mechanisms are attached to their respective frames at differentpoints along the width 1686 of the frames. Staggering the attachmentlocation of the drive mechanisms to the frames may help to reduce thespace between each of the drive mechanisms (in the directionperpendicular to the drawing plane) so that the space occupied by thecollimator may be more compact. FIG. 16G depicts an assembly of fourleaves and drive mechanisms which may be repeated and scaled up toinclude as many leaves as may be desired for a collimator. For example,a collimator may have 16, 32, 64, 128 or more leaves each with their owndrive mechanisms.

While some collimator leaf drive mechanisms may comprise a spring systemand an actuator system having a pneumatic or a slotted link mechanism,other drive mechanisms may comprise an electromagnetic actuator system.An electromagnetic actuator system may comprise a movable member towhich the leaf is attached, a first coiled assembly and a second coiledassembly separated by a gap to the first coiled assembly. The movablemember may be located within the gap, and movable between the first andsecond coiled assemblies. The current through the coils of each coiledassembly generates a magnetic field, and the direction and magnitude ofthe field depend on the magnitude and direction of the applied current.When it is desired to retain the leaf in the open or the closedconfiguration, one coiled assembly (e.g., either the first or the secondcoiled assembly) may be activated by applying a current through itscoils to hold the movable member against that coiled assembly. To retainthe leaf in the closed or open configuration, the other coiled assembly(e.g., either the second or the first coiled assembly) may be activatedby applying a current through its coils to hold the movable memberagainst that coiled assembly. Some variations may comprise one or morepermanent magnets that may be configured to retain the leaf in the openor closed configurations without drawing any electrical power. Forexample, the movable member may comprise a permanent magnet. In othervariations, one or more electromagnets may be used and the amount ofelectrical power supplied to those electromagnets to hold the leaf inthe open or closed configurations may be determined at least in part bythe amount of magnetic force needed to counteract the forces generatedby the spring system. Electromagnetic actuator systems may includevariable reluctance actuators, such as linearized variable reluctanceactuators.

One variation of an electromagnetic actuator system that may be used inconjunction with a spring system (such as any described herein) in amulti-leaf collimator is depicted in FIGS. 17A-17E. Electromagneticactuator system 1700 may be a variable reluctance actuator and maycomprise a movable member 1702 located between a first coiled assembly1704 and a second coiled assembly 1706 that is separated from the firstcoiled assembly by a gap 1701. A collimator leaf 1711 (schematicallyrepresented in FIG. 17B) may be attached to the movable member 1702. Themovable member 1702 moves within the gap 1701 between the first andsecond coiled assemblies depending on the cumulative forces on themovable member from the first and second coiled assemblies and thespring system, as shown in FIG. 17E. The movable member 1702 (to which acollimator leaf may be attached) may be attached to a movable mount1720. The movable mount 1720 may comprise a first spring attachmentportion 1722 a located at a first end of the movable mount and a secondspring attachment portion 1722 b located at a second end of the movablemount. The spring system may comprise a first spring 1703 a and a secondspring 1703 b. The first and second springs may be coil springs (asdepicted in FIG. 17E), or may be any type of spring as describedpreviously. A first end of the first spring 1703 a may be attached tothe first spring attachment portion 1722 a of the movable mount and asecond end of the first spring 1703 a may be attached to a first springmount 1724 a. A first end of the second spring 1703 b may be attached tothe second spring attachment portion 1722 b of the movable mount and asecond end of the second spring 1703 b may be attached to a secondspring mount 1724 b. The first and second spring mounts 1724 a,b may befixedly attached to a base (e.g., a mounting plate, board, or substrate)such that the springs mounts 1724 a,b, the first coiled assembly 1704and the second coiled assembly 1706 are stationary relative to themovable member 1702 and the movable mount 1720. The size of the gap 1701may be selected to correspond to the travel distance of the leaf fromthe open configuration to the closed configuration, and in somevariations, may be greater than or equal to the desired beam width. Forexample, the gap 1701 may be from about 12 mm to about 15 mm. The sizeof the gap may be selected to compress and/or expand the one or moresprings of the spring system to add potential energy to the springsystem that is at least equal to (and may optionally be greater than)the spring forces that were lost during the motion of the springs andthe leaf and/or movable member (e.g., energy losses due friction, drag,etc.). Each coiled assembly may comprise a first coil having a firstlumen and a second coil having a second lumen, and a core that extendsthrough both the first and second lumens. For example, as depicted inFIGS. 17A, 17B and 17D, the first coiled assembly 1704 may comprise afirst coil 1708 a having a first lumen 1709 a, a second coil 1708 bhaving a second lumen 1709 b, and a C-shaped core 1710 that extendsthrough both the first and second lumens. The first and second ends ofthe C-shaped core may extend through the lumen of the coils (see, forexample, FIG. 17B), or may be flush with the opening of the lumen of thecoils. The coils may comprise copper, aluminum, silver, gold, carbonnanotubes or other conducting materials, any of which may have a round,square, rectangular, or ribbon-like cross-section. For example, thecoils may have a cross-sectional shape where the width is greater thanthe thickness/height of the coil, and/or may be one or more strips,sheets, ribbons, braids, etc. of the materials described above. The coremay comprise laminated steel, solid steel, laminated steel alloys, orsolid steel alloys. The movable member 1702 may comprise laminatedsteel. The movement of the movable member 1702 may be a function of thedistance of the movable member to the first coiled assembly, thedistance of the movable member to the second coiled assembly, and theelectromagnetic force generated by each of the first and second coiledassemblies, in addition to the forces exerted on the movable member fromthe spring system. The closer the movable member is to a coiledassembly, the greater the attractive force exerted on the movable memberby that coiled assembly. The force (either attractive or repulsive,depending on the direction of the current) generated by a coiledassembly that is exerted on the movable member may be non-linearlyrelated to the position of the movable mass relative to the coiledassembly and the current through the coils of the coiled assembly (e.g.,the force may be inversely proportional to the gap between the coiledassembly and the movable member, and proportional to the currentsquared). For example, the electromagnetic actuator system 1700 may bean opposed unipolar variable reluctance actuator. When it is desired toretain the leaf in the open or the closed position, one coiled assembly(e.g., either the first or the second coiled assembly) may be activatedby applying a current through its coils to hold the movable member 1702against that coiled assembly. To retain the leaf in the closed or openposition, the other coiled assembly (e.g., either the second or thefirst coiled assembly) may be activated by applying a current throughits coils to hold the movable member 1702 against that coiled assembly.

Another variation of an electromagnetic actuator system is depicted inFIGS. 18A and 18B. The electromagnetic actuator system 1800 may besimilar to the system 1700 depicted in FIGS. 17A-17D (like numbersrepresent like elements), and the description for system 1700 may alsoapply for system 1800. Similarly, a collimator leaf may be attached tothe movable member 1802 as depicted in FIG. 17B. The system 1800 maycomprise a movable member 1802 comprising a permanent magnet 1803. Thepermanent magnet 1803 may be located anywhere on the movable member, forexample, may be located within the movable member (e.g., permanentmagnet core), and/or along the surface of the movable member. In somevariations, a movable member may comprise a plurality of permanentmagnets, which may be arranged linearly along a length of the movablemember, entirely enclosed within the movable member, partially enclosedwithin the movable member, on the surface of the movable member,symmetrically or asymmetrically arranged, on one or both ends of themovable member, etc. The permanent magnet 1803 may act to linearize theforce (either attractive or repulsive, depending on the direction of thecurrent) generated by a coiled assembly that is exerted on the movablemember. That is, the generated force may be linearly related to theposition of the movable mass 1802 relative to the activated coiledassembly and the current through the coils of the activated coiledassembly. This linearizing effect may be more pronounced when the sizeof the gap 1801 smaller than the smallest dimension of thecross-sectional shape of the end portion 1811 of the core 1810 (e.g.,the width of the gap is less than about 20%, or less than about 10%, orless than about 5% or less than about 2% or less than about 1% of thesmallest dimension of the end portion 1811 of the core), and may be lessapplicable when the gap 1801 is similar to the pole face dimension(e.g., the width of the gap is greater than about 50%, or greater thanabout 70%, or greater than about 75%, or greater than about 80%, orgreater than about 90% of the smallest dimension of the end portion 1811of the core). In addition, the permanent magnet 1803 in the movablemember 1802 may allow the system 1800 to retain the leaf in either theclosed or open configuration without driving a current through thecoiled assemblies, which may help to reduce the power consumption of thesystem 1800. To release the movable member 1802 from the coiled assemblyto which it is magnetically attached (for instance, the first coiledassembly) so that the leaf may transition from one configuration to theother, a current with the appropriate magnitude and direction may beapplied to the first coiled assembly so that the attractive forcebetween the first coiled assembly and the movable member is reduced(e.g., the repulsive force between them is increased), which may thenallow the forces from the spring assembly to move the movable memberaway from the first coiled assembly towards the second coiled assembly.

FIGS. 19A-19C depict various electromagnetic actuation systems thatcomprise one or more permanent magnets. The actuation systems 1900,1920, 1940 may be similar to the actuation system 1700 depicted in FIGS.17A-17D, and may each comprise a movable member located in a gap betweena first coiled assembly and a second coiled assembly. A collimator leafmay be attached to the movable member, as schematically depicted in FIG.17B. The electromagnetic actuation system 1900 may comprise a firstcoiled assembly 1902 having first and second coils with a first core1906 disposed within the lumens of the first and second coils, and asecond coiled assembly 1904 having first and second coils with a secondcore 1908 disposed within the lumens of the first and second coils. Thefirst core 1906 and the second core 1908 may each comprise a permanentmagnet 1910, 1912. For example, the first and second cores may beC-shaped, and a permanent magnet may be located along the verticallength of the “C” (e.g., located along the length of the core that spansthe gap between the first coil and the second coil of the coiledassembly). Alternatively or additionally, one or more permanent magnetsmay be located at the ends of the C-shaped core. For example, theelectromagnetic actuation system 1920 may comprise a first coil assembly1922 and a second coil assembly 1924, where the first coil assembly 1922comprises a first C-shaped core 1923, a first permanent magnet 1926 aand a second permanent magnet 1926 b, and the second coil assemblycomprises a second C-shaped core 1925, a third permanent magnet 1928 a,and a fourth permanent magnet 1928 b. The first permanent magnet 1926 amay be located at a first end of the core 1923 and the second permanentmagnet 1926 b may be located at a second end of the core 1923. The thirdpermanent magnet 1928 a may be located at a first end of the core 1925and the fourth permanent magnet 1928 b may be located at a second end ofthe core 1925. The permanent magnets 1926 a,b and 1928 a,b may cover atleast a portion of the surface of the end of the cores 1923, 1925, ormay cover the entire surface of the end of the cores. Alternatively oradditionally, the movable member may comprise one or more permanentmagnets that are located on the surface of the movable member. Forexample, the electromagnetic actuation system 1940 may comprise amovable member having a first permanent magnet 1941 a, a secondpermanent magnet 1941 b, a third permanent magnet 1941 c, a fourthpermanent magnet 1941 d located on the surface of the movable member. Inthis variation, the first permanent magnet 1941 a is located on themovable member such that it is aligned with a first end surface of theC-shaped core of the first coil assembly and the second permanent magnet1941 b is located on the movable member such that it is aligned with asecond end surface of the C-shaped core of the first coil assembly. Thethird permanent magnet 1941 c is located on the movable member such thatit is aligned with a first end surface of the C-shaped core of thesecond coil assembly and the fourth permanent magnet 1941 d is locatedon the movable member such that it is aligned with a second end surfaceof the C-shaped core of the second coil assembly.

Optionally, a multi-leaf collimator using any of the leaf drivemechanisms described herein may comprise a return or recoil spring suchthat the spring system and/or actuator system moves the leaf in onedirection while the recoil spring moves the leaf in the oppositedirection. This may help to simply the mechanics of the leaf drivemechanism so that the mechanism provides a force in just one directionwhile the recoil spring provides a force in the opposite direction. Insome variations, this may reduce the number of components for the leafdrive mechanism and allow for a more compact collimator. For example,the spring system and/or actuator system of a leaf drive mechanism maybe configured to move the leaf from the closed position to the openposition, where the applied force stores potential energy in a recoilspring. Once the spring system or actuator system is in a state thatallows the leaf to move, the recoil spring then uses the potentialenergy to move the leaf from the open position back to the closedposition. Alternatively, the leaf actuation mechanism may be configuredto move the leaf from the open position to the closed position and therecoil spring may be configured to move the leaf from the closedposition to the open position. The return or recoil spring may be a coilspring, torsion spring, or torsion bar. Some variations may comprise aplurality of recoil springs in parallel. The spring distortion may beextension, compression, or some combination thereof across multiplesprings. Although this arrangement may require the spring system and/oractuator system of the leaf drive mechanism to be capable of applying aforce against the recoil spring in order to transition the leaf from afirst position to a second position (which may double the force of thattransition), no additional force is needed to transition the leaf fromthe second position back to the first position.

While the drive mechanisms disclosed herein are described in the contextof moving collimator leaves for a high bandwidth binary multi-leafcollimator, it should be understood that such drive mechanisms may bealso be used in other systems. For example, such drive mechanisms may beused to move the leaves of a collimator for conformal radiotherapyand/or IMRT.

What is claimed as new and desired to be protected by Letters Patent ofthe United States is:
 1. A collimator comprising: a leaf movable betweena first position and a second position; a leaf shaft having a proximalportion and a distal portion, and wherein the distal portion of theshaft is attached to the leaf; a spring system coupled to the leaf; andan actuator system coupled to the leaf shaft, wherein a motive forcegenerated by the spring system and a motive force generated by theactuator system longitudinally translate the leaf from the firstposition to the second position, and wherein the actuator system isconfigured to selectively retain the leaf at the first position or thesecond position, and wherein the actuator system comprises a barrelcomprising a longitudinal lumen, a first side opening, and a second sideopening, and a piston located within the longitudinal lumen of thebarrel, wherein the piston comprises the shaft and a piston seal coupledto the shaft within the barrel, and wherein movement of the pistonwithin the barrel translates the leaf between the first position and thesecond position, and wherein the movement of the piston is controlled byfluid flow through the first and second side openings.
 2. The collimatorof claim 1, wherein the motive force generated by the actuator system issufficient to overcome losses in the spring system.
 3. The collimator ofclaim 1, wherein the actuator system has a first configuration whereinthe leaf is retained in the first position and a second configurationwherein the leaf is retained in the second position.
 4. The collimatorof claim 1, wherein the spring system comprises a first spring disposedalong a first length of the shaft and a second spring disposed along asecond length of the shaft, the first and second springs configured suchthat the piston seal moves between the first side opening and the secondside opening.
 5. The collimator of claim 4, wherein the first spring andthe second spring are located within the barrel lumen.
 6. The collimatorof claim 5, wherein the first spring is in contact with the piston on afirst side and the second spring is in contact with the piston on asecond side that is opposite the first side.
 7. The collimator of claim4, wherein the first spring is located outside of the barrel lumenbetween a spring retainer and a first end wall of the barrel.
 8. Thecollimator of claim 1, further comprising a fluid source connected tothe first side opening and the second side opening.
 9. The collimator ofclaim 8, further comprising a first valve between the first side openingand the fluid source and a second valve between the second side openingand the fluid source, wherein the first and second valves selectivelyregulate fluid flow into and out of the barrel lumen.
 10. The collimatorof claim 8, wherein the fluid source comprises a pressurized air source.11. The collimator of claim 8, wherein injecting fluid from the fluidsource into the first side opening and not the second side openingcauses the piston to move the leaf to the first position.
 12. Thecollimator of claim 8, wherein injecting fluid from the fluid sourceinto the second side opening and not the first side opening causes thepiston to move the leaf to the second position.
 13. The collimator ofclaim 12, wherein injecting fluid into the second side opening comprisescreating sufficient pressure to hold the leaf in the second position.14. The collimator of claim 1, wherein the spring system comprises atleast one coil spring.
 15. The collimator of claim 5, wherein the pistonis configured to contact the first spring and not the second spring whenthe leaf is in the first position and to contact the second spring andnot the first spring when the leaf is in the second position.
 16. Thecollimator of claim 9, further comprising a controller in communicationwith the fluid source, the first valve and the second valve, wherein thecontroller is configured to open and close the first valve and thesecond valve to selectively regulate fluid flow into and out of thebarrel lumen.
 17. The collimator of claim 16, wherein the controller isconfigured to move the leaf to the first position by opening the firstvalve to the fluid source.
 18. The collimator of claim 17, wherein thecontroller is configured to open the second valve to atmosphericpressure prior to opening the first valve to the fluid source.
 19. Thecollimator of claim 16, wherein the controller is configured to move theleaf to the second position by opening the second valve to the fluidsource.
 20. The collimator of claim 19, wherein the controller isconfigured to open the first valve to atmospheric pressure prior toopening the second valve to the fluid source.
 21. The collimator ofclaim 1, wherein the spring system comprises at least one torsion barspring.
 22. The collimator of claim 11, wherein injecting fluid into thefirst side opening comprises creating sufficient pressure to hold theleaf in the first position.
 23. The collimator of claim 17, wherein thecontroller is configured to open the second valve to the fluid sourcewhen the leaf is at or near the first position to reduce piston speed.24. The collimator of claim 19, wherein the controller is configured toopen the first valve to the fluid source when the leaf is at or near thesecond position to reduce piston speed.
 25. The collimator of claim 1,wherein the spring system is coupled to the leaf shaft.
 26. Thecollimator of claim 25, wherein the spring system and the actuatorsystem are coupled to the proximal portion of the leaf shaft.
 27. Thecollimator of claim 26, wherein the spring system and the actuatorsystem are attached to the proximal portion of the shaft.
 28. Thecollimator of claim 1, wherein the motive force generated by the springsystem and the motive force generated by the actuator systemlongitudinally translate the leaf from the second position to the firstposition.
 29. The collimator of claim 1, wherein the spring system andthe actuator system are configured to translate the leaf from the firstposition to the second position in about 10 ms or less.
 30. Thecollimator of claim 29, wherein the spring system and the actuatorsystem are configured to translate the leaf from the first position tothe second position in about 6 ms or less.